With water levels in Spain’s Valdecañas reservoir drained to 28 percent capacity, a sprawling prehistoric monument has emerged from the dry lake bed: the “Spanish Stonehenge,” also known as the dolmen of Guadalperal. The massive megalithic complex is believed by archeologists to date back to 5000 B.C., according to Reuters. Rediscovered in modern times by German researcher Hugo Obermaier in 1926, the structure has only fully popped up out of the waters four times since then. “It’s a surprise,” expert Enrique Cedillo told Reuters, “it’s a rare opportunity to be able to access it.” Little is known about the civilization that erected them, nor what they were for, with popular theories including that they were grave-markers, trading posts, ritual sites, or dire water-level warnings, prophesying famines to come. The dolmen was last visible in 2019. The peninsula where the structure is erected is at its driest point in 1,200 years, with conditions expected to worsen, according to a study cited by Reuters.