Our main hope, when our cruise started in the early afternoon, had been to see proboscis monkeys and that was achieved within a few minutes of leaving the small wharf in our long, lean riverboat.
We rounded a bend in the river to find a huge, fat, two-storey jerrybuilt craft, belching diesel smoke and loaded with jolly passengers seated at tables, pushed close to the bank.
Our lean machine slid easily inside the monster and we enjoyed a great view of a proboscis family enjoying their evening meal in an adjacent tree.
The dominant male - the massive nose that is his status symbol clearly silhouetted against the sky - sat at the top of the tree, munching on tender young leaves. From time to time, when he had eaten out one branch, he would lean over, grab another and pull it up to within easy picking distance.
His small harem of females, easily distinguished with their smaller, upturned noses, at least a couple of them with youngsters in tow, were dotted around the rest of the tree chewing with enthusiasm.
It was a delightful scene, but after a while the diesel fumes from our big neighbour became a bit much, so we moved on.
Further downriver, we found another proboscis family and a small group of bachelor males, a family of macaques also enjoying a bedtime snack and a young macaque who seemed to be all alone on the river bank.
Watching a family of macaques, in particular, was reminiscent of human bedtime. The adults would wedge themselves into the fork of a tree for the night, only for the youngsters to decide they weren't ready to settle down and scamper off down the branch.
Their long-suffering mothers would dash in pursuit and bring the youngsters back to bed for the night, where they might finally drop off ... or not.
We watched this pantomime, and a similar performance by a proboscis family, until it was too dark to see anything. And then the fireflies came out.
But our adventure was far from over when we got back to the riverboat base. First there was a long bus drive through the countryside, past the inevitable flames of forest being burned off - unusually, with a fire engine in attendance - and through villages also settling down for the night, to the local port.
There we boarded the Orion's Zodiacs for a spectacular voyage through the Labuan islands - a notable anchorage for centuries past - past the bright lights of oil rigs and settlements back to our ship. It was a thrilling trip - especially when water starting pouring in the back of the Zodiac.
In fact, when we saw the lights of Orion sparkling - like fireflies - right in front of us, we all gave a spontaneous cheer.
CHECKLIST
Getting there: Singapore Airlines flies up to three times daily from New Zealand to Singapore and then beyond to Bandar Seri Begawan five times a week. The airline's regional service, SilkAir, flies to several destinations in Borneo, including Kuching (three times a week), Kota Kinabalu (daily) and Balikpapan (six flights a week).
Further information: See Orion Expedition Cruises.
Jim Eagles visited Borneo with help from Singapore Airlines and Orion Expedition Cruises.
