Dusk was fast approaching in Bandar Seri Begawan, but the speedboat defiantly charged down the capital's Brunei River in search of wild proboscis monkeys.

Ten minutes after leaving the jetty, passing wooden houses on stilts, mosques with glittering golden domes and the enormous Nurul Iman palace on its banks, the boat arrived at the mangrove forest.

There, against the crimson sky, dozens of the endangered monkeys with light brown fur perched lazily on a single tree. The pot-bellied male with its pendulous nose dozed contentedly among his harem of 10 females, many nursing their babies.

"When the tide is low, you can also see quite a number of crocodiles sunbathing here, and the macaque coming down," said tour guide Dayangku Kemariah Pengiran Haji Duraman.

"You can see herons sitting on the crocodile and the macaque teasing the crocodile or throwing fruits or branches at it. Some evenings if we are lucky, we can see the wild boars scavenging by the mangrove banks."

Brunei, a tiny energy-rich sultanate in Borneo, is tapping its tourism potential as it seeks to cut reliance on oil and gas, which has been fuelling its economy for decades.

It is promoting its lush rainforests and pristine waters as ecotourism destinations, organising festivals to generate excitement and building new infrastructure, including a 30km-long bridge linking its urban capital to the rainforest hinterland.

The two regions are currently separated by Malaysia's Sarawak and accessible only by boat.

By 2020, the government wants to double air arrivals to 451,000.

Mr Zamree Junaidi, tourism development department director at the Ministry of Primary Resources and Tourism, told The Straits Times that tourism brought B$178.6 million (S$178.6 million) to the country of half a million people last year.

This target is significant, considering annual tourist air arrivals have plateaued in the last decade and now hover between 157,000 and 242,000 a year.

451k Number of air arrivals Brunei hopes to bring in by 2020.

WHAT TO DO AND WHERE TO GO

BANDAR SERI BEGAWAN • Take a boat ride to a "water village", where 11,000 residents live in houses built on stilts on the river • Zip aboard a speedboat to a mangrove forest along the Brunei River to see the endangered proboscis monkeys native to Borneo and Sumatra • Visit Jame' Asr Hassanil Bolkiah Mosque with its 29 golden domes, and Omar Ali Saifuddien Mosque • Check out Royal Regalia Building for a collection of royal gifts and relics and historical artefacts • Feast on local food at Tamu Gadong night market TEMBURONG • Camp at Freme Rainforest Lodge and have a go at the flying fox, rock climbing and abseiling • Trek in the Ulu Temburong National Park with an Iban villager • Climb Canopy Tower to catch the sunrise • Try other outdoor activities such as kayaking and water-tubing TUTONG • Visit Kiudang Village for its well-preserved rainforest and a gallery showcasing antiques, handicrafts and musical instruments. The village won the Asean community-based tourism award at the Asean Tourism Forum in Singapore this year. • Shop at the Thursday market for local delicacies and cottage-industry products • Cruise along the river to see wildlife such as crocodiles, monkeys and birds, as well as local fishermen netting their daily catch MUARA • For diving enthusiasts, choose from 60 dive sites, 30 shipwrecks and even a decommissioned oil rig. The sea life here includes barracudas and trevallys. Arlina Arshad

OIL SLUMP

Decades ago, before the list of world's richest men was dominated by the chiefs of tech giants Amazon, Facebook, Microsoft and Oracle, the Sultan of Brunei Hassanal Bolkiah was among the wealthiest.

But today, as oil prices struggle to climb above US$60 a barrel, let alone touch their one-time high of US$100 again, Brunei has begun to look elsewhere to boost its income.

The Muslim-majority country, which has followed strict Islamic laws since 2014, is no country for partying, shopping and entertainment. Even the sale of alcohol and smoking in public are banned.

There are malls in the city, but none carries major retail labels. Underdeveloped public transport makes private cars essential.

The town centre goes quiet after 9pm, though some restaurants stay open 24 hours. Even locals would rather take long drives to nearby Sarawak and Sabah during the weekend for leisure and shopping.

But ecotourism brims with potential. More than two-thirds of the 5,765 sq km land, or roughly eight times the size of Singapore, is covered in pristine rainforests, home to native primates, pangolins and 622 species of birds. Off the coast, divers can explore over 60 sites and some 30 shipwrecks.

Dr Mario Hardy, chief executive of the non-profit trade association Pacific Asia Travel Association, noted Brunei's "beautiful unspoiled nature parks, walking trails and beaches".

"I realised that this may not be the first thing that comes to mind when people think of Brunei. For anyone who has taken the time to explore some of the lesser-known areas of the country, I can tell you that there is much to discover," he added.

"Brunei is a small gem that has yet to be discovered by many."

But it is making progress. The World Economic Forum's travel and tourism competitiveness report published in April ranked Brunei among the top 10 fastest-growing destinations for leisure travel from 2016 to 2026.

Mr Zamree said the country's small size allows travellers to see it in a few days. They can also enjoy the fresh air, peaceful atmosphere and few traffic jams.

NATURE HAVEN

Tourists from Asean countries make up the bulk of visitors to the "Kingdom of Unexpected Treasures", as Brunei is known. Singaporeans are the fifth-largest source market, with more than 14,000 visitors last year.

Ms Justine Koh, marketing communications executive from Singapore tour agency Chan Brothers, said Brunei is an "underrated destination" among Singaporeans seeking culture and, increasingly, water sports overseas.

"It's not a destination chockful of activities for the average tourist but rather a peaceful and safe country with a relatively slow pace of living. It is increasingly known for its fabulous diving sites," she said.

Mr Zamree said the government is hoping to receive more travellers from Europe and Asia.

After all, Brunei's offerings are not cheap compared with tour packages to similar destinations in neighbouring Malaysia and Indonesia. Brunei's currency is pegged to the Singapore dollar, making it the strongest in South-east Asia.

"We do realise that we are on the higher side but we are targeting a different market segment," Mr Zamree said, claiming that higher prices have not deterred tourists from neighbouring countries.

Numbers have, in fact, risen over the years as Brunei has "its own niche and speciality", he said.

South Korean Kim Mia, who travelled with her family to Brunei in October, said the cost of her vacation was "reasonable", adding: "We enjoy swimming and climbing here."

Mr William Tan, 53, a Singaporean underwater photographer, said "super-rare marine creatures are quite common in Brunei waters" as the government has strict rules to protect them. And, he added, since there are still relatively few divers in the area, "marine creatures here do not show fear when you close in to take images of them."

To entice Bruneians to stay in the country for their year-end holidays, the government is rolling out its first major Brunei December Festival, featuring food tasting, automotive show and motorcross challenge, among other activities.

Mr Kamarul Ajimain, 47, a social and digital multimedia manager, said that being relaxed does not mean his country is boring.

"We're not trying to compete with our neighbours. The focus is more on nature and taking a step back from the usual hustle and bustle.

"I call it a place to do nothing."

As the government moves to attract local and foreigner tourists, local communities express their excitement over the developments.

Boatman Dom Anak Moi, 61, who lives in Temburong, where the bridge is being built, said he will need to drive only 30 minutes to the capital for his weekly grocery shopping once the bridge is ready in 2019. Now, he spends two hours, including going through Malaysian immigration.

"The pages in my passport run out so quickly with all the Malaysia stamps, but I have no choice. Going by boat takes even longer."

"With the bridge, Brunei will truly become one."