It’s not quite Atlantis, but it could be Aquaman’s summer getaway.

Archeologists in Turkey have discovered an ancient fortress half-buried at the bottom of the country’s largest lake, where the alkaline waters have kept the structure well-preserved for approximately 3,000 years.

The lost fortress is thought to have been built millennia ago on the shores of Lake Van, back when the Urartu civilization populated that area of the Armenian Highlands. Water levels have risen by several hundred metres since that time, and the fortress is believed to have been abandoned as a result.

The lost castle was discovered by divers working for a team of researchers from Van Yüzüncü Yil University, who were initially hunting for the mythical Lake Van Monster. The structure’s walls stand approximately 3-4 metres high, and its structural footprint is believed to be approximately 1 kilometre wide.

“Archeologists and museum authorities told us that there was nothing we would find,” lead diver Tahsin Ceylan told Turkey’s Anadolu news agency.

It’s not the first submerged secret to be discovered in Lake Van. A Russian shipwreck from 1948 was discovered at the bottom of the lake in July, and previous discoveries have included a four-kilometre-square field of stalagmites and a gravesite from 1,000 years ago. Researchers have also found artifacts from previous civilizations at shallower depths in the lake.

Archeologists say more work is necessary to determine the full size of the structure, and to verify that it was indeed built by the Urartu people.

The Urartu, also known as the Kingdom of Van, ruled over the region during the Iron Age for approximately 300 years before they were invaded by the Medes people.

Video shot by Ceylan and shared with National Geographic shows divers investigating the site.