Tham Khoun Xe is a swimming cave on Route 12 east of Thakhek, where a river emerges from a cave mouth into a pool. The water is clear and cool, and the cave can be entered for swimming in the first section where natural light still reaches. It is a standard stop on the Thakhek Loop and makes an appealing midday break — the combination of cave, cool water, and limestone scenery is hard to improve on in terms of a place to stop for a swim.
The site has basic facilities and a small entrance charge. Bring footwear that can get wet for the cave section, and a headlamp if you want to explore beyond the illuminated entrance. It is easily combined with several other caves along the same stretch of highway into a half-day cave circuit from Thakhek.