Minecraft: It is FunAugust 08, 2009
Minecraft is a browser-based, first-person construction game, currently free-to-play in alpha. As it's so easily accessable and multiplayer-ready, it's about equivalent to an afternoon of messing about with Legos with one's peers: Incredibly Fun.
Here is an invisible kitten that I made.
Well, translucent, at least.
We spent at day making things out of cheese. These are just... samples.
Cheese skywalks (and other constructions) can cast interesting shadows. Grass only grows in the sun, and other materials interact in different ways.