If beach is not your thing, climbing the Mt. Kinabalu might be an option to enjoy your stay in Malaysia. Juts keep in mind that a permit is required to climb the Mountain and a guide is compulsory.
Lyan recently did part of the trail and send me this card.
The Farmers' Brand
Mt Kinabalu (4095m) is the tallest mountain in South-East Asia and is situated in the Kinabalu National Park in the province of Sabah in Malaysian Borneo. Thousands of tourists visit Kinabalu National Park each year and most come with the intention of climbing Mt Kinabalu.
Fortunately, Mt Kinabalu is one of the easiest peaks in the world to conquer. It takes just two days and climbers don't need any previous experience at mountain climbing. At sunrise, the views from the Mt Kinabalu's summit at Low's Peak are spectacular, making all the effort worthwhile.
Most climbers take two days to ascend and descend Mt Kinabalu. The eight-kilometre climb generally starts from the the Timpohon Gate near park headquarters (1800m), with an overnight stay at one of the guest houses at Laban Rata (3273m), before pushing on to the summit early next morning. Mt Kinabalu's summit is usually reached in time to view the sunrise, before returning to Laban Rata for breakfast. Climbers then descend the mountain, generally reaching the park headquarters by mid-afternoon. - in: http://www.climbmtkinabalu.com/