A young backpacker, Ricardo Machado Oliveira, was exploring a remote mountain cave and while in it apparently blacked out. When he came to, he found himself in a vast underground hangar surrounded by "three distinct species of aliens." Nearby were several ovoid silvery craft. The aliens told Ricardo that they were part of an alliance of interstellar worlds engaged in observing Earth. Their base under the Serra da Guardunha was one of four such bases. Immediately after hearing this Ricardo blacked out again. When he opened his eyes, he was lying on the ground right outside the cave. (In the 14th century, at the same cave, a little girl from a nearby village vanished for three days. When she was finally found, she told the search party that she had been cared for by "a lady in white", who had offered her water to drink from a bell. Some have attributed this to a visitation by the Blessed Virgin Mary.)

Google map of this location.