Nearby the Kinabatangan area are the Gomantong Caves; one of the biggest cave systems in Sabah. The caves are part of the Gomantong Forest Reserve (3000ha). In this enormous cave you will find many millions of bats during the day and just as many swiftlets (family of the swallow) at night. In the evening you can witness the bats flying out and the swiftlets flying into the cave again (same goes for the mornings). The feces of both birds form a feeding ground (guano) for millions of dung beetles and cockroaches, which makes walking through the caves a less pleasant experience for many. Unsurprisingly, the cave smells heavily like ammonia.
These caves also house snakes that feed themselves with the cockroaches. Gomantong actually consists of two caves, the black cave and the white cave. The black cave (90mtr) can easily be visited by tourists. The white cave is not easily accessible. A walk through the cave will not leave your shoes unaffected; although there is a boardwalk to walk on. We had to throw away our shoes after a visit to Gomantong, so we would recommend putting plastic bags over your shoes (or by some throw-away shoes just for the cave visit).
Another place to see in Malaysia: Stunning Rawa island