The Gomantong Caves are vast limestone cavities inhabited by swiftlets whose nests are harvested twice a year (normally Feb–April and July–Sept) for the bird’s-nest-soup trade. The caves are also home to a huge number of bats, and the enormous piles of guano (droppings) give them a distinctive acrid smell.
There are two main caves. The black cave, smaller but only a ten-minute walk from the ticket office, mostly contains black nests, a combination of twigs and bird saliva. The white cave is rarely visited by tourists as it’s another hour away, but nest collectors go there for the more valuable white nests, made from pure saliva. Note that the guano attracts a huge number of cockroaches, so don’t wear flip-flops or sandals.
There’s nowhere to stay or eat in and around Gomantong, so plan to leave the caves well before dark if you are not on a tour.