My son and his wife camped out for 3 nights in Vietnam's Son Doong Cave, thought to be the world's largest cave (in volume). The caverns could comfortably hold a 747 airplane. The cave
has a river and a primaeval forest, and it has its own ecosystem. It was first discovered in 1990 but not surveyed until 2009.

The colors of the cave make up the palette of the color challenge.