Nestled between the Arenal and Tenorio volcanoes, this heart-shaped crater lake is widely recognized in ufology as the site of the most scientifically vetted Unidentified Aerial Phenomenon (UAP) photograph ever taken. On September 4, 1971, at exactly 8:25 AM, a twin-engine Aero Commander aircraft flying at 10,000 feet was conducting an official aerial mapping survey for the National Geographic Institute of Costa Rica to plan the Arenal hydroelectric project. Mounted to the floor of the plane was a specialized, 100-pound German mapping camera programmed to snap high-resolution black-and-white negatives automatically at precise intervals. It was only after processing the film that frame #300 revealed a massive, metallic, disc-shaped object with a raised central dome seemingly hovering over, or emerging from, the lake’s northern shoreline. The craft appeared in only one frame of the sequence, completely absent from the pictures taken mere seconds before and after, indicating blinding operational speed or instant cloaking capabilities. The negative remained strictly within government hands, but leaked copies eventually reached prominent international scientists, including Dr. Jacques Vallée and Dr. Richard Haines. Extensive digital drum scans and forensic photo-analysis by organizations like Ground Saucer Watch confirmed the anomaly was a physical, solid object estimated at 160 feet in diameter that was not a product of double exposure, lens flare, or fabrication. Beyond this single snapshot, the lake has a centuries-old reputation as an active “portal” for Unidentified Submerged Objects (USOs), with the indigenous Maleku people traditionally honoring the crater as a sacred gateway to alternate dimensions. Local farmers and workers at nearby eco-lodges consistently document bizarre, glowing green light-rings hovering directly over the water at night, alongside rhythmic surface wakes that move against the prevailing mountain winds.