The Naupa Huaca cave in Peru has a mysterious alter or false door made of andesite rock, with modern Inca work off to the side. Though it is not clear how the creators of the structure cut such precise ninety-degree angles into the rock, it is possible that softer stones like flint or fulgurite were used instead of machines.

While closer examination with a microscope shows some chiseling was used to cut out the structure, obsidian was also melted onto the andesite rock, though it is unclear how the ancient people managed to do this. Historically, false doors were used as alters for mourning the dead, with the ancient Incas placing their dead in an upright position and having them sit in the alter for ritual purposes. Some suggest that these structures were actually portals to bring the deceased into the afterlife, but the exact purpose remains unclear.