There is s an underground chamber in Vercetti Estate below the pool. The chamber is solid, meaning a player using modifications can land in the room without falling into the Ghost World, technically making it a room. The entrance to the chamber is unknown, but few myth hunters have put forward their theories regarding the purpose of the chamber.
According to technical gamers, the chamber is used for unused reflections in the pool area and this is the most accepted theory. Upon closer inspecting, the columns and arches in the chamber match perfectly with those in the pool room. Furthermore, this has been theorized to be a crypt for Ricardo Diaz's Ghost or an unknown entity, but this remains unknown and is likely to be false.