That little speck with the light is a person. The main chamber is more than 5 kilometers (3.1miles) long, 200m (660ft) high and 150m (490ft) wide. At this scale, a half-mile block of 40-story buildings could fit inside this lit stretch of Hang Son Doong cave. The cave features two collapsed dolines, or sinkholes, that let daylight in. This has given life to the cave, making it possible for two separate forests to grow within it, a feature not normally associated with the subterranean recesses.