Trung Trang Cave is the largest limestone cave on Cát Bà Island, sitting inside the national park 17km from Cát Bà town. The cave runs approximately 300 metres into the karst hillside with two main chambers connected by a passage, and it's dense with stalactite and stalagmite formations that have built up over thousands of years.
The name and the history layered into the cave are both worth knowing before you walk in. The cave was originally called Hang Dơi - Bat Cave - for its resident colony. During the resistance wars it was used as a military base and became known as Hang Hải Quân (Navy Cave), with traces of that occupation still visible inside today.
The name Trung Trang comes from an older local legend: Bà Chúa Trung Trang, a woman who rallied the island's young men to repel foreign invaders, then retreated to the cave to guard the island. The villagers named the cave after her in her honour.