Though not fully submerged, the "Underwater City" in Bulgaria is "a town built in the middle of a lake, not on an island, but actually below water level." Click here for one more picture.
This is going to be done via the construction of a huge circular dike that'll be a whopping 1,377 feet in diameter and 65 feet high. People will be able to access the recessed city by boat, heading down into it to see the city.[via Gizmodo]