The majority of treks , either on the Malaysian Peninsula or in Sarawak and Sabah, require some forethought and preparation, and you should be prepared for trails and rivers to become much more difficult to negotiate when it rains. That said, although the rainy season (Nov-Feb) undoubtedly slows your progress on some of the trails, conditions are less humid and the parks and adventure tours not oversubscribed. Most visitors trek in the large national parks to experience the remaining primary jungle and rainforest at first hand. For these you often need to be accompanied by a guide, which can either be arranged through tour operators in Kuala Lumpur, Kuching, Miri and Kota Kinabulu, or at the parks themselves. For inexperienced trekkers, Taman Negara is probably the best place to start, while Sarawak's Gunung Mulu offers sufficient challenges for most tastes, and few people who make it across to Sabah forego the chance of climbing Mount Kinabalu, not a task to be undertaken lightly, however.