The Mulu National Park houses some stunningly beautiful rainforest and the largest caves on the planet. The park is easily reached by plane from Kota Kinabalu or Miri; accommodation at Park HQ is excellent but fairly basic whereas the Royal Mulu Resort offers luxury.
There is a wide variety of forest walks, one of the longest canopy walks in the world, caving trips for 'normal' tourists or more adventurous ones (including into the largest underground chamber on earth), a spectacular bat flight, river trips and wildlife nightwalks. It's so fabulous it's a world heritage site.
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