The Santubong jungle trail is maintained by the Holiday Inn resorts but open to all. The trail branches out into the mountain trek where a trekker can climb Mount Santubong (810m) in about six hours.
The jungle trail itself is a one to two hours trek, depending on pace. I would recommend applying insect repellent except that it seemed to attract more mosquitoes instead (this observation is verified by a local guide). The jungle is dense but the trail is well-marked (look for the blue markings at the tree barks; red is for mountain trekkers).
I had made my way as far as the waterfall, taking about half an hour to reach it before turning back. It had rained heavily the night before, making the trail wet and slippery. The trail requires one to wade through the pool just afer the waterfall or jump across mossed covered boulders at the top of the waterfall. As I was trekking alone, I did not want to take the risk. Nevertheless, it was an enjoyable trek that offered a glimpse of Borneo's lush primary rainforest.