I really liked the reflections example (reflect.ray), but I wanted some more diffuse objects, so I added the rods. One of our bells was placement of objects inside other objects, so I really wanted to show that off with the pink sphere inside the yellow one.

Another bell was making the tracer threaded. This really speeds it up in release mode. This 512x512 rendering took 5.343 seconds (with 60 threads).

Depth was set at 10.

Render times:
5.343 seconds with 60 threads
5.703 seconds with 30 threads
5.516 seconds with 20 threads
5.609 seconds with 15 threads
6.078 seconds with 4 threads
5.984 seconds with 2 threads
12.171 seconds with 1 thread (the stock time)