Nong Khai Aquarium

The reason to come here is the Mekong itself. Rather than the usual imported reef fish, the tanks are stocked with species from the river system running past Nong Khai, which makes the visit feel like it belongs where it is. The walk-through tunnel is the bit children remember, with fish passing overhead and at eye level while you stand underneath.

It's a modest place, not a day out in its own right, and I'd budget a couple of hours rather than half a day. Families with young kids get the most from it, along with anyone who's spent time looking at the Mekong from a promenade and wondered what actually lives in all that brown water. The displays lean educational, so it also works well on a hot afternoon when you want a roof over your head and something for the children to do. If you have no interest in fish, skip it and spend the time on the riverfront instead.