Further examples of internal DSLs
Many internal DSLs look like good object oriented design. Good quality is invisible. A design pattern is a MEANS that should cash out in simplicity, not an end in itself.
Recipes in a minecraft-like game: https://github.com/Miserlou/Minicraft/blob/master/src/com/mojang/ld22/crafting/Crafting.java
The OpenGL interface: http://www.opengl.org/archives/resources/code/samples/glut_examples/examples/cube.c
The Cairo interface: http://www.cairographics.org/samples/
JMock-style fluent interfaces: https://github.com/mikeando/Fluent-Interface-Test
SIGPLAN / interpreter design pattern