Several treks are possible in the basin, ranging from short nature walks around Agathis Research Station to the multiday slog to the rim of the basin via Strike Ridge Camp. The vast majority of visitors undertake a five-day, four-night loop through the southern section of the basin that we'll call the Maliau Loop. Shorter packages restrict visitors to just a taste of Maliau Basin around the Maliau Basin Studies Centre and Agathis Camp.
The Maliau Loop trek will likely be the most memorable hike of your Borneo experience. It vies with the Salt Trail for the title of Sabah's toughest trek. It takes in wide swaths of diverse rainforest and four of the basin's waterfalls: Takob Falls, Giluk Falls, the stupendous, seven-tiered Maliau Falls and Ginseng Falls. It's not for novices: there are several strenuous, steep hill climbs, rivers to ford and stretches of dense forest that require machete use. You'll be trekking around 7km per day (six to eight hours). Do not attempt the trek unless you are in excellent shape (adventure-tour operators insist that your travel insurance policy covers a helicopter evacuation and a fitness certificate from your doctor).
The density of the old-growth forest is striking, and as it is more remote than the Danum Valley, the preserved wildlife is even better. Eighty species of mammals (and counting) have been recorded here, including clouded leopard, Sumatran rhino, Malayan sun bear, pygmy elephant, Bornean gibbon, red- and grey-leaf monkeys and banteng. That said, you will be in dense primary forest, where wildlife is not easy to spot. You may walk away without seeing anything (unlikely) except for some of Borneo's most ancient trees, though the night drives around Maliau Basin Studies Centre (MBSC) give you a good opportunity to spot nocturnal mammals. During treks you'll be looking out for langurs, gibbons, birds, frogs and reptiles.
A canopy walkway stretches near the MBSC, and it is pretty astounding to walk its length amid rainforest canopy that has never felt a human cut. Bird-watchers tend to go up there at dawn.