Yak Lom Lake is Banlung's number-one attraction. It is a volcanic crater filled with fresh water, surrounded by a trail that takes about an hour to walk. The lake has mystical significance to local people. There is a pier from which you can swim and inner tubes are available to rent. The entrance fee is $1. There is also a visitor center, which displays some local handicrafts and has information on local tribes and some good walks in the area. Yak Lom Lake is 5km (3 miles) from Banlung heading east. It is an hour's walk or you can hire a moto for $1 each way plus a tip if you make him wait any length of time.
There are a number of waterfalls around Ratanakiri, some of which are easily accessible from Banlung. Chha Ong waterfall is west of Banlung on National Rd. 78. It is purported to be the highest in Ratanakiri at 30m (98 ft.). You can swim at the foot of the falls. Entrance is 2,000 riel. Katieng waterfall, Kah Chhang waterfall, and Bai S'rok waterfall are other nearby waterfalls worth a stop. Katieng is often considered to be the most fun because you actually clamber under a rock shelf and behind the flow of the water a bit like Daniel Day-Lewis in The Last of the Mohicans.
At Bai S'rok there is still a lot of gem-mining activity although that might be diminishing since the whole area is getting pretty much mined out. You can combine a visit with an elephant ride and a village home stay -- ask at your guesthouse.
Lumkut Lake is another beautiful cratered lake situated in dense forest near Borkeo district about 30km (19 miles) north of Banlung. You can swim here, but not in rainy season when the dirt path that leads there is virtually impassable. With a guide, the trip should cost about $15 per person for a half-day trip and can include a stop in a Tampuan minority village.
Virachey National Park is a wild area teeming with wildlife that has yet to be fully explored. All trips to Virachey have to be arranged through the park service and accompanied by an approved guide. You can sort this out through your guesthouse or you can go directly to the ranger's office and arrange the trip with them. The park headquarters is located 3 blocks north of the post office. The most popular trek is the 3-day trip, which includes spending 1 night inside a hut adjacent to an ethnic Brou village just outside the park, and 1 night spent in a hammock about 20km (12 miles) inside the park boundary. It is about a 30km (19-mile) walk total and costs $107 per person, though the price can come down with groups that have more than two people.
The central market of Psar Banlung is the place to see Khmer Loeu people arrive early in the morning carrying "back strap" baskets laden with vegetables, fruit, and forest products, which they sell at the market. It can be a fascinating and photogenic scene. It is all over by 10am. The Reclining Buddha at Wat Rahtanharahm sits at the base of Eisey Patamak Mountain about 1km (1/2 mile) east of town. The views from here are fantastic.