There is really cool geology being explored on large, oddly shaped asteroids. The Near Earth Asteroid Rendezvous (NEAR) mission reached 433 Eros in 2000, and one of the exciting results was the discovery of features called "ponds".
Time to open the eleventh door in the advent calendar. Until the New Year, I'll be opening a door onto a different landscape from somewhere in the solar system. Where in the solar system are these sinuous ridges?