Seshat's Sunken Temple
A shoreline ruin in Madiama Nome.
Three treasures here, all of them underwater. The farthest out is just on the seafloor- a small red chest by the remains of wall.
For the middle one, you'll need to dive down through the big square hole near the marker, then swim southeast.
For the last, enter the underwater passage that leads right under the temple itself, and bear left at the crocodile statue.
Snag this last treasure from a large red chest to complete the location, and don't forget you can fast travel while underwater.