Three thousand years ago, Turkey’s largest lake, Lake Van, wasn’t even a puddle, but several millennia have washed away the memories of any civilization that once resided there… but that’s the great thing about archaeology. A group of divers who have been exploring the floor of the lake have stumbled upon a 3,000 year old sunken fortress that stood above water during the Iron Age.

The team undertook the expedition after hearing rumors of the ruins, but they were not expecting to find something on the scale of what they uncovered. What they found was an archaeological site that is around a half a mile, square, with castle walls that still stand 10-13 feet above the bottom.

So, who used to live there? The researchers believe it was probably the Urartu, a kingdom held power during the 9th-6th century BCE. That’s pretty much all we know for now as deeper excavations will begin to find out how much of the castle is yet to be uncovered.