A 45 minutes boat-ride from Muara lies Pulau Selirong (Selirong Island), which is a 2,566 hectares mangrove-covered island. There is a 2 kilometres of wooden walkways offering close-up views of the mangroves and wildlife. There is also an observation tower and the island has toilet facilities and rest huts.

For years, this jewel of nature has served as a nature preserve park dedicated to protect its rich forest heritage and the unique flora and fauna that thrive on the island. Quite strangely, Brunei's wealth of oil and natural gas has saved the country from depending on cultivating in the forest areas and thus it can now boast of virtually untouched forests. That is certainly evident when the lush mangroves that reach up to 40 meters into the sky greet the eyes. In fact, when compared to the ordinary mangroves growing in other places, they are nearly twice as tall and thick.

Of course, when traveling to Pulau Selirong, one can't miss out on the opportunity to explore the wonderful wildlife roaming around the towering mangroves. All one needs to bring is some gear, food, and more important, lots of patience. Probably the most common sight is the so-called "colugo," or the flying lemurs that are usually hanging upside-down on tree branches. It is ironic, however, that, despite their name, they can't actually fly (they instead glide using the extra skin between their limbs), and are not even real lemurs for that matter.

One can also catch a glimpse of the flights of exotic birds, mammals, and snakes. The forest comes alive with a cacophony of various sounds, ranging from the calls of the cicadas to the cries of the jumping prawns. Despite these, the highlight to any visit to the island is the rare Orang Belanda, better known as the proboscis monkey. Seen almost exclusively in the vicinity of Borneo, it can be easily distinguished because of its large protruding nose from whence it got its name.