From time to time I run into a site full of pictures or stories that inspire me. I’ve included a few links to such sites in the past.
Subterranean Design is one that check out every time I get a post in my aggregator.
Subterranean Design, as I have mentioned before (and put in the Hall of Fame under Sources of Inspiration) is a wonderful source of evocative pictures. I’ve been posting mostly pictures of caves and caverns, but there are quite a few man-made structures (especially mines, vaults, and various tunnels, including sewer tunnels) as well. Some of them end up fairly creepy and I can easily see using them for supernatural adventures or games.
Mind you, they don’t restrict themselves to just underground locations. They also include other pictures of ruins and similar sites.