I am just flabbergasted by how gorgeous this series of caves, tunnels, pools, etc. is, built by Warren Ludwig over a the LUDstuff blog. If you have any interest in miniatures, terrain, etc. or just want to see something incredibly cool come to life, do yourself a favor and pop over there; he has a six-part series of posts on the blog that detail the entire process from inspiration to finished product, with tons of advice and photos.
See that liiiiitle figure near the bottom of the photo? That'll give you some idea of the scale of this project. Absolutely incredible. Makes me want to start using minis in my regular RPG game again.