Gunung Mulu National Park also became a UNESCO World Heritage Site in 2000, because of its spectacularly dramatic karst limestone landscapes. And with karst comes caves. Not just poke your head in and shout for echoes caves, but seriously wacky 'Sarawackian' caves. Such as Clearwater, where only 12 people at a time are guided through 1.5km of subterranean scapes, with crabs, snakes, bats and all. Or Deer Cave which is one of the largest cave passages in the world, where your otherworldly expedition finishes with you not only coming back out for air, but the huge colonies of bats that inhabit them joining you, in search for their almost by clockwork evening feast of flying insects. Another gem is the Sarawak Chamber, accessible after a three hour hike, wading down a river canyon, then up a bouldered slope to one of the largest enclosed spaces on earth. Now that is a trip.