Thien Duong — known in English as Paradise Cave — is the national park's most spectacular accessible cave, and the most popular destination after Son Doong. A boardwalk leads 1 kilometre into a cathedral-scale passage, with stalactites and stalagmites in extraordinary formations covering the floor and ceiling. The lighting is restrained, which is unusual for Vietnamese show caves, and the scale only becomes apparent as you move deeper into the passage and the entrance disappears behind you.
The cave is 31 kilometres long in total, making it one of the longest dry caves in Asia. On the VIP tour (a separate booking), you can walk the first seven kilometres beyond the standard boardwalk with a guide, which takes about five hours and involves more demanding terrain. The deeper sections have formations the standard tour doesn't reach. Either way, allow at least two hours for the full boardwalk and the walk from the car park. The cave maintains a constant cool temperature — bring a light layer if you get cold easily.