31350997[single built works by location: topographical]PT2026-03-30 20:34:42BT31323623single built works by location or contextPTNT31381919cave architecturePTNT31381922earthworksPTNT31381926extraterrestrial structuresPTNT31381930rock-cut architecturePTNT31381936hillside architecturePTNT31381949marine structuresPTNT31381953underground structuresPTNT31381958underwater buildingsPTNT31381963earthen architecturePTNT31381967artificial islandsPTNT31381970artificial reefsPT