So, if you had access to a server cluster, what would you do with it?

I'm thinking render farm; I've always liked 3D rendering. Or perhaps bitcoin mining. But I'm new to this, and there are most likely many options I'm overlooking. Please feel free to reply, or note me if it's better kept private. If you know of anyone who works with networks, ask 'em. It's an interesting question. :)

I'm talking about dozens of servers that aren't being used for anything, and won't be. If I have a good cause, I may be able to do something with them.