Tham Yai Nam Nao (Phu Nam Rin)

Tham Yai Nam Nao is a limestone cave inside Nam Nao National Park in the Phetchabun highlands, reached via a turnoff at kilometre 60 of Highway 2216. The surveyed system runs 9,817 metres through five entrances — one of the longest documented caves in Thailand — but the section open to casual visitors is a lit, 400-metre walking loop through the entrance chambers, about an hour round trip. It’s part of Nam Nao rather than a stand-alone free attraction, so the park’s standard entrance fee applies here too.

The entrance chambers hold stalactites and stalagmites built up over a long span of time, with flowstone curtains and columns reaching from floor to ceiling. Cool, damp air replaces the highland heat outside almost immediately past the mouth of the cave, and water still drips audibly from the ceiling in places. The park protects a resident bat colony here, including rarer species alongside more common ones — expect to hear them shift in the dark sections beyond the lit walkway. Electric lighting covers the main loop; side passages leading deeper into the 9.8km system stay unlit and are not part of the standard visit.

Watch out: the lit loop is only a small fraction of the full cave. Park staff at the protection unit, about 3km past the highway turnoff, can arrange a guide if you want to see more than the entrance chambers — don’t wander into unlit side passages alone.

Insider Tip: go in the morning. The walk in from the road and the checkpoint queue are more comfortable before the midday heat builds on the approach road, and the cave itself stays a constant cool regardless of what time you arrive.

Cave floors are uneven and can be slippery near the drip lines, so wear shoes with actual grip rather than sandals. A light jacket helps — the temperature inside sits noticeably below the highland air outside, which is already cooler than lowland Thailand. Bring a torch if you want to examine formations in the dimmer stretches; the fixed lighting is functional rather than bright. Pair the visit with the rest of Nam Nao National Park, since you’ll already be paying the park’s entrance fee to reach the cave.