diff --git a/src/main/java/ch/fritteli/labyrinth/Labyrinth.java b/src/main/java/ch/fritteli/labyrinth/Labyrinth.java
index c8baa80..93d19a9 100644
--- a/src/main/java/ch/fritteli/labyrinth/Labyrinth.java
+++ b/src/main/java/ch/fritteli/labyrinth/Labyrinth.java
@@ -1,14 +1,17 @@
 package ch.fritteli.labyrinth;
 
 import io.vavr.control.Option;
+import lombok.Getter;
 import lombok.NonNull;
 
 import java.util.Deque;
 import java.util.LinkedList;
 
 public class Labyrinth {
-    final Tile[][] field;
+    private final Tile[][] field;
+    @Getter
     private final int width;
+    @Getter
     private final int height;
 
     public Labyrinth(final int width, final int height) {
@@ -41,34 +44,35 @@ public class Labyrinth {
     private void hardenWalls(@NonNull final Tile tile, final int x, final int y) {
         if (x == 0) {
             tile.preventDiggingToOrFrom(Direction.LEFT);
-        } else if (x == width - 1) {
+        } else if (x == this.width - 1) {
             tile.preventDiggingToOrFrom(Direction.RIGHT);
         }
         if (y == 0) {
             tile.preventDiggingToOrFrom(Direction.TOP);
-        } else if (y == height - 1) {
+        } else if (y == this.height - 1) {
             tile.preventDiggingToOrFrom(Direction.BOTTOM);
         }
     }
 
     private void generate() {
-        new Generator();
+        new Generator().run();
     }
 
-    public class Generator {
+    private class Generator {
         private final Deque<Position> positions = new LinkedList<>();
 
-        Generator() {
+        void run() {
+            this.preDig();
+            this.dig();
+            this.postDig();
+        }
+
+        private void preDig() {
             final Position bottomRight = new Position(Labyrinth.this.width - 1, Labyrinth.this.height - 1);
             final Tile bottomRightTile = Labyrinth.this.getTileAt(bottomRight);
             bottomRightTile.enableDiggingToOrFrom(Direction.BOTTOM);
             bottomRightTile.digFrom(Direction.BOTTOM);
             this.positions.push(bottomRight);
-            this.dig();
-            final Position topLeft = new Position(0, 0);
-            final Tile topLeftTile = Labyrinth.this.getTileAt(topLeft);
-            topLeftTile.enableDiggingToOrFrom(Direction.TOP);
-            topLeftTile.digTo(Direction.TOP);
         }
 
         private void dig() {
@@ -94,5 +98,12 @@ public class Labyrinth {
                 }
             }
         }
+
+        private void postDig() {
+            final Position topLeft = new Position(0, 0);
+            final Tile topLeftTile = Labyrinth.this.getTileAt(topLeft);
+            topLeftTile.enableDiggingToOrFrom(Direction.TOP);
+            topLeftTile.digTo(Direction.TOP);
+        }
     }
 }
diff --git a/src/main/java/ch/fritteli/labyrinth/TextRenderer.java b/src/main/java/ch/fritteli/labyrinth/TextRenderer.java
index be16a91..7b60640 100644
--- a/src/main/java/ch/fritteli/labyrinth/TextRenderer.java
+++ b/src/main/java/ch/fritteli/labyrinth/TextRenderer.java
@@ -1,33 +1,19 @@
 package ch.fritteli.labyrinth;
 
-import lombok.Builder;
+import lombok.AccessLevel;
+import lombok.AllArgsConstructor;
+import lombok.NoArgsConstructor;
 import lombok.NonNull;
-import lombok.Value;
-import lombok.With;
+import lombok.experimental.FieldDefaults;
 import org.jetbrains.annotations.Nullable;
 
 public class TextRenderer {
-    static final String HORIZONTAL = "\u2500";
-    static final String VERTICAL = "\u2502";
-    static final String LEFT = "\u2574";
-    static final String UP = "\u2575";
-    static final String RIGHT = "\u2576";
-    static final String DOWN = "\u2577";
-    static final String DOWN_RIGHT = "\u250c";
-    static final String DOWN_LEFT = "\u2510";
-    static final String UP_RIGHT = "\u2514";
-    static final String UP_LEFT = "\u2518";
-    static final String VERTICAL_RIGHT = "\u251c";
-    static final String VERTICAL_LEFT = "\u2524";
-    static final String HORIZONTAL_DOWN = "\u252c";
-    static final String HORIZONTAL_UP = "\u2534";
-    static final String CROSS = "\u253c";
     private final Labyrinth labyrinth;
     private final int width;
     private final int height;
     private int x = 0;
     private int y = 0;
-    private int border = 0;
+    private int line = 0;
 
     private TextRenderer(@NonNull final Labyrinth labyrinth, final int width, final int height) {
         this.labyrinth = labyrinth;
@@ -36,11 +22,11 @@ public class TextRenderer {
     }
 
     public static String render(@NonNull final Labyrinth labyrinth) {
-        final int width = labyrinth.field.length;
+        final int width = labyrinth.getWidth();
         if (width == 0) {
             return "";
         }
-        final int height = labyrinth.field[0].length;
+        final int height = labyrinth.getHeight();
         final TextRenderer renderer = new TextRenderer(labyrinth, width, height);
 
         final StringBuilder sb = new StringBuilder();
@@ -54,135 +40,200 @@ public class TextRenderer {
         return this.y < this.height;
     }
 
+    private Tile getTileOrNull(final int x, final int y) {
+        if (x < 0 || y < 0 || x >= this.width || y >= this.height) {
+            return null;
+        }
+        return this.labyrinth.getTileAt(x, y);
+    }
+
     private String next() {
         final Tile currentTile = this.labyrinth.getTileAt(this.x, this.y);
-        final Tile leftTile = this.x > 0 ? this.labyrinth.getTileAt(this.x - 1, this.y) : null;
-        final Tile topTile = this.y > 0 ? this.labyrinth.getTileAt(this.x, this.y - 1) : null;
-        String s = "";
-        switch (this.border) {
+        final Tile leftTile = this.getTileOrNull(this.x - 1, this.y);
+        final Tile topTile = this.getTileOrNull(this.x, this.y - 1);
+        final String s;
+        switch (this.line) {
             case 0:
-                s = this.renderTop(currentTile, leftTile, topTile);
+                s = this.renderTopLine(currentTile, leftTile, topTile);
                 break;
             case 1:
-                s = this.renderCenter(currentTile);
+                s = this.renderCenterLine(currentTile);
                 break;
             case 2:
-                s = this.renderBottom(currentTile, leftTile);
+                s = this.renderBottomLine(currentTile, leftTile);
+                break;
+            default:
+                s = "";
                 break;
         }
         // do some magic ...
         this.x++;
         if (this.x == this.width) {
             this.x = 0;
-            this.border++;
+            this.line++;
         }
-        if (this.border == 2 && this.y < this.height - 1) {
-            this.border = 0;
+        if (this.line == 2 && this.y < this.height - 1) {
+            this.line = 0;
             this.y++;
         }
-        if (this.border == 3) {
-            this.border = 0;
+        if (this.line == 3) {
+            this.line = 0;
             this.y++;
         }
         return s;
     }
 
-    private String renderTop(@NonNull final Tile currentTile, @Nullable final Tile leftTile, @Nullable final Tile topTile) {
-        final CharDefinition.CharDefinitionBuilder builder1 = CharDefinition.builder();
-        final CharDefinition.CharDefinitionBuilder builder2 = CharDefinition.builder();
-        final CharDefinition.CharDefinitionBuilder builder3 = CharDefinition.builder();
+    private String renderTopLine(@NonNull final Tile currentTile, @Nullable final Tile leftTile, @Nullable final Tile topTile) {
+        final CharDefinition charDef1 = new CharDefinition();
+        final CharDefinition charDef2 = new CharDefinition();
+        final CharDefinition charDef3 = new CharDefinition();
         String result;
         if (currentTile.hasWallAt(Direction.LEFT)) {
-            builder1.down(true);
+            charDef1.down();
         }
         if (currentTile.hasWallAt(Direction.TOP)) {
-            builder1.right(true);
-            builder2.left(true).right(true);
-            builder3.left(true);
+            charDef1.right();
+            charDef2.horizontal();
+            charDef3.left();
         }
         if (currentTile.hasWallAt(Direction.RIGHT)) {
-            builder3.down(true);
+            charDef3.down();
         }
         if (leftTile != null && leftTile.hasWallAt(Direction.TOP)) {
-            builder1.left(true);
+            charDef1.left();
         }
         if (topTile != null) {
             if (topTile.hasWallAt(Direction.LEFT)) {
-                builder1.up(true);
+                charDef1.up();
             }
             if (topTile.hasWallAt(Direction.RIGHT)) {
-                builder3.up(true);
+                charDef3.up();
             }
         }
-        result = builder1.build().toString() + builder2.build();
+        result = charDef1.toString() + charDef2;
         if (this.x == this.width - 1) {
-            result += builder3.build() + "\n";
+            result += charDef3 + "\n";
         }
         return result;
     }
 
-    private String renderCenter(@NonNull final Tile currentTile) {
-        final CharDefinition.CharDefinitionBuilder builder1 = CharDefinition.builder();
-        final CharDefinition.CharDefinitionBuilder builder2 = CharDefinition.builder();
+    private String renderCenterLine(@NonNull final Tile currentTile) {
+        final CharDefinition charDef1 = new CharDefinition();
+        final CharDefinition charDef2 = new CharDefinition();
         String result;
         if (currentTile.hasWallAt(Direction.LEFT)) {
-            builder1.up(true).down(true);
+            charDef1.vertical();
         }
         if (currentTile.hasWallAt(Direction.RIGHT)) {
-            builder2.up(true).down(true);
+            charDef2.vertical();
         }
 
-        result = builder1.build() + " ";
+        result = charDef1 + " ";
 
         if (this.x == this.width - 1) {
-            result += builder2.build() + "\n";
+            result += charDef2 + "\n";
         }
 
         return result;
     }
 
-    private String renderBottom(@NonNull final Tile currentTile, @Nullable final Tile leftTile) {
+    private String renderBottomLine(@NonNull final Tile currentTile, @Nullable final Tile leftTile) {
         String result;
-        final CharDefinition.CharDefinitionBuilder builder1 = CharDefinition.builder();
-        final CharDefinition.CharDefinitionBuilder builder2 = CharDefinition.builder();
-        final CharDefinition.CharDefinitionBuilder builder3 = CharDefinition.builder();
+        final CharDefinition charDef1 = new CharDefinition();
+        final CharDefinition charDef2 = new CharDefinition();
+        final CharDefinition charDef3 = new CharDefinition();
 
         if (currentTile.hasWallAt(Direction.LEFT)) {
-            builder1.up(true);
+            charDef1.up();
         }
         if (currentTile.hasWallAt(Direction.BOTTOM)) {
-            builder1.right(true);
-            builder2.left(true).right(true);
-            builder3.left(true);
+            charDef1.right();
+            charDef2.horizontal();
+            charDef3.left();
         }
         if (currentTile.hasWallAt(Direction.RIGHT)) {
-            builder3.up(true);
+            charDef3.up();
         }
         if (leftTile != null && leftTile.hasWallAt(Direction.BOTTOM)) {
-            builder1.left(true);
+            charDef1.left();
         }
 
-        result = builder1.build().toString() + builder2.build();
+        result = charDef1.toString() + charDef2;
 
         if (this.x == this.width - 1) {
-            result += builder3.build();
+            result += charDef3;
         }
         return result;
     }
 
-    @Value
-    @Builder
-    @With
+    @FieldDefaults(level = AccessLevel.PRIVATE)
+    @NoArgsConstructor
+    @AllArgsConstructor
     static class CharDefinition {
-        @Builder.Default
+        // ─
+        static final String HORIZONTAL = "\u2500";
+        // │
+        static final String VERTICAL = "\u2502";
+        // ╴
+        static final String LEFT = "\u2574";
+        // ╵
+        static final String UP = "\u2575";
+        // ╶
+        static final String RIGHT = "\u2576";
+        // ╷
+        static final String DOWN = "\u2577";
+        // ┌
+        static final String DOWN_RIGHT = "\u250c";
+        // ┐
+        static final String DOWN_LEFT = "\u2510";
+        // └
+        static final String UP_RIGHT = "\u2514";
+        // ┘
+        static final String UP_LEFT = "\u2518";
+        // ├
+        static final String VERTICAL_RIGHT = "\u251c";
+        // ┤
+        static final String VERTICAL_LEFT = "\u2524";
+        // ┬
+        static final String HORIZONTAL_DOWN = "\u252c";
+        // ┴
+        static final String HORIZONTAL_UP = "\u2534";
+        // ┼
+        static final String CROSS = "\u253c";
         boolean up = false;
-        @Builder.Default
         boolean down = false;
-        @Builder.Default
         boolean left = false;
-        @Builder.Default
         boolean right = false;
 
+        CharDefinition up() {
+            this.up = true;
+            return this;
+        }
+
+        CharDefinition down() {
+            this.down = true;
+            return this;
+        }
+
+        CharDefinition vertical() {
+            return this.up().down();
+        }
+
+        CharDefinition left() {
+            this.left = true;
+            return this;
+        }
+
+        CharDefinition right() {
+            this.right = true;
+            return this;
+        }
+
+
+        CharDefinition horizontal() {
+            return this.left().right();
+        }
+
         public String toString() {
             if (this.up) {
                 if (this.down) {
diff --git a/src/main/java/ch/fritteli/labyrinth/Tile.java b/src/main/java/ch/fritteli/labyrinth/Tile.java
index 20695f7..3ac0a80 100644
--- a/src/main/java/ch/fritteli/labyrinth/Tile.java
+++ b/src/main/java/ch/fritteli/labyrinth/Tile.java
@@ -3,16 +3,12 @@ package ch.fritteli.labyrinth;
 import io.vavr.collection.Stream;
 import io.vavr.control.Option;
 import lombok.AccessLevel;
-import lombok.Getter;
 import lombok.NonNull;
 import lombok.experimental.FieldDefaults;
 
 @FieldDefaults(level = AccessLevel.PRIVATE)
 public class Tile {
-    // FIXME remove me; only for debugging
-    @Getter
     final Walls walls = new Walls();
-    @Getter
     boolean visited = false;
 
     public Tile() {
diff --git a/src/test/java/ch/fritteli/labyrinth/TextRendererTest.java b/src/test/java/ch/fritteli/labyrinth/TextRendererTest.java
index 9453876..b5ed6de 100644
--- a/src/test/java/ch/fritteli/labyrinth/TextRendererTest.java
+++ b/src/test/java/ch/fritteli/labyrinth/TextRendererTest.java
@@ -1,27 +1,32 @@
 package ch.fritteli.labyrinth;
 
+import ch.fritteli.labyrinth.TextRenderer.CharDefinition;
+import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class TextRendererTest {
-    @Test
-    void charDefTest() {
-        assertEquals(" ", new TextRenderer.CharDefinition(false, false, false, false).toString());
-        assertEquals("╶", new TextRenderer.CharDefinition(false, false, false, true).toString());
-        assertEquals("╴", new TextRenderer.CharDefinition(false, false, true, false).toString());
-        assertEquals("─", new TextRenderer.CharDefinition(false, false, true, true).toString());
-        assertEquals("╷", new TextRenderer.CharDefinition(false, true, false, false).toString());
-        assertEquals("┌", new TextRenderer.CharDefinition(false, true, false, true).toString());
-        assertEquals("┐", new TextRenderer.CharDefinition(false, true, true, false).toString());
-        assertEquals("┬", new TextRenderer.CharDefinition(false, true, true, true).toString());
-        assertEquals("╵", new TextRenderer.CharDefinition(true, false, false, false).toString());
-        assertEquals("└", new TextRenderer.CharDefinition(true, false, false, true).toString());
-        assertEquals("┘", new TextRenderer.CharDefinition(true, false, true, false).toString());
-        assertEquals("┴", new TextRenderer.CharDefinition(true, false, true, true).toString());
-        assertEquals("│", new TextRenderer.CharDefinition(true, true, false, false).toString());
-        assertEquals("├", new TextRenderer.CharDefinition(true, true, false, true).toString());
-        assertEquals("┤", new TextRenderer.CharDefinition(true, true, true, false).toString());
-        assertEquals("┼", new TextRenderer.CharDefinition(true, true, true, true).toString());
+    @Nested
+    class CharDefinitionTest {
+        @Test
+        void testRendering() {
+            assertEquals(" ", new CharDefinition(false, false, false, false).toString());
+            assertEquals("╶", new CharDefinition(false, false, false, true).toString());
+            assertEquals("╴", new CharDefinition(false, false, true, false).toString());
+            assertEquals("─", new CharDefinition(false, false, true, true).toString());
+            assertEquals("╷", new CharDefinition(false, true, false, false).toString());
+            assertEquals("┌", new CharDefinition(false, true, false, true).toString());
+            assertEquals("┐", new CharDefinition(false, true, true, false).toString());
+            assertEquals("┬", new CharDefinition(false, true, true, true).toString());
+            assertEquals("╵", new CharDefinition(true, false, false, false).toString());
+            assertEquals("└", new CharDefinition(true, false, false, true).toString());
+            assertEquals("┘", new CharDefinition(true, false, true, false).toString());
+            assertEquals("┴", new CharDefinition(true, false, true, true).toString());
+            assertEquals("│", new CharDefinition(true, true, false, false).toString());
+            assertEquals("├", new CharDefinition(true, true, false, true).toString());
+            assertEquals("┤", new CharDefinition(true, true, true, false).toString());
+            assertEquals("┼", new CharDefinition(true, true, true, true).toString());
+        }
     }
 }