Three highly recommended experiences:
1) try Bako National Park near Kuching. It's easy and surprisingly fascinating. Try getting a boat to the far end and hiking back.
2) the pinnacles. Stiff climb up near Mulu to razor sharp limestone peaks. It's a long day so you camp near the base. Need a guide too from memory. (a bit harder)
3) try taking the weekly plane into a mountain village like Long Lelang and living with in a Kelabit Longhouse for a week. We were fortunate to be 'adopted' by a couple of local chiefs and guided around up there for some months. (awesomely hard and risky and dangerous and one of the best experiences I've ever had)
Enjoy almost 6 years ago