If you google "room under lake" you'll find info on what I would consider is an exquisite piece of architecture built in like the 1880s. It's a half dome built in an artificial lake with a statue on the top of the dome. It's pretty neat looking with elegant tunnels leading to and from the room. The current owner of the property doesn't seem to maintain or use the structure at all, which is a real shame. When you realize that this was built well over 100 years ago by a scam artist who was wealthy but not particularly so. Imagine what a modern billionaire with modern construction techniques could build. For instance, I'm told one of the walmart heirs has a crazy underground fortress.