Off the shores of a tiny island in the middle of the vast Pacific Ocean are the ruins of an ancient civilization. The remains of Nan Madol are the only standing monument of a civilization built entirely over open water, on a coral reef.

The eerie abandoned stone structures are said to have inspired science-fiction writer H. P. Lovecraft to create a similar sunken city that was home to the monster Cthulhu, says Atlas Obscura.

In reality, Nan Madol was once home to the Saudeleur, who ruled the island of Pohnpei for more than a millennium, reported Smithsonian Magazine. The 92 artificial islands of Nan Madol are thought to have been constructed over the course of several centuries, and then eventually abandoned after 1,000 years of habitation.

Rufino Mauricio, Pohnpei’s only archaeologist, has dedicated his life to studying and preserving the ruins, which are built of 750,000 tons of black basaltic rock.

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“We don’t know how they brought the columns here and we don’t know how they lifted them up to build the walls. Most Pohnpeians are content to believe they used magic to fly them,” Mauricio told Smithsonian.

He added that given the size of Pohnpei’s population at the time — fewer than 30,000 people — the construction of Nan Madol is an even larger and more remarkable effort than the Great Pyramids were for the ancient Egyptians.

Although Mauricio would like to clear out all the brush that now covers the small islands, preservation has become a complicated issue because of the ownership of Nan Madol. Although it belongs to the state of Pohnpei in the Federated States of Micronesia, the traditional leader of the municipality where Nan Madol is located doesn’t want to relinquish control, making protection from UNESCO difficult to achieve.

For now, the ruins remain isolated from the rest of the island, avoided by the locals who fear that disturbing the site will bring bad luck, says Archaeology magazine.

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The three large pyramids of Menkaure (L), Khafre (C) and Khufu loom over the horizon November 13, 2004 at Giza, just outside Cairo, Egypt. The three large pyramids at Giza, built by King Khufu over a 30 year period around 2,550 B.C., are among Egypt's biggest tourist attractions. (Sean Gallup/Getty Images)