- The Hollow Earth is an obsolete concept proposing that the planet Earth is entirely hollow or contains a substantial interior space. Notably suggested by Edmond Halley in the late 17th century, the notion was disproven, first tentatively by Pierre Bouguer in 1740, then definitively by Charles Hutton in his Schiehallion experiment around 1774.
- Lake Titicaca (Wikipedia)
Lake Titicaca (/tɪtɪˈkɑːkə/; Spanish: Lago Titicaca [ˈlaɣo titiˈkaka]; Quechua: Titiqaqa Qucha) is a large freshwater lake in the Andes mountains on the border of Bolivia and Peru. It is often called the highest navigable lake in the world. Titicaca is the largest lake in South America both in terms of the volume of water and surface area. It has a surface elevation of 3,812 m (12,507 ft).