The Son Doong Cave in Vietnam is currently the largest-known cave on Earth. It was first discovered by a local in 1991, and surveyed by the British Cave Research Association from April 10 to April 14, 2009. Its largest chamber is over five kilometers in length, 200 meters high and 150 meters wide.
Game and Story Use
- Just because it was "officially discovered" in 1991/2009, it doesn't mean that nobody knew of this cave before, or that the entire cave complex has been explored. What might be hidden in its chambers? Lost civilizations of subterranean creatures? Temples to the Great Old Ones? Caches of weapons from the Vietnam War?
- With suitable additions, the initial exploration of the cave might make a great Call of Cthulhu scenario - the explorers are surrounded by a strange culture and thus isolated socially as well as physically from the rest of the world, some of the natives might be hostile (perhaps they are even Tcho-Tcho - it's the right region), and they might get trapped in the cave with monsters or worse.
- If the real world has caves large enough to house entire cities, fantasy and science fiction settings can easily justify them as well.