"OSRS" stands for "Old School RuneScape," which is a massively multiplayer online role-playing game (MMORPG). "What Lies Below" is a quest in OSRS that deals with the Dagonhai, an order of powerful Zamorakian mages. The quest involves teaming up with the Dagon'hai to stop a plot by a rogue member of the order to summon Zamorak himself. The quest takes place in various locations, including the Varrock Palace Library, the Outlaw Camp, and the Chaos Altar. Therefore, there is no physical location "below" OSRS.