See the largest cave in the bay, opened by the French in 1901

Surprise Cave, and it was

Tour boats scattered on flat grey water between limestone islands in thick haze, seen through bare branches — Andre Hospers · CC BY 4.0

A wooden walkway curves round a small bay of jade water below a forested karst, boats moored beyond — Andre Hospers · CC BY 4.0

A lit path with wooden handrails winds through a wide cavern of stalactites and flowstone — lumoplank · CC0

A vast cave chamber lit gold from below, a paved path curving across its floor past massive columns — Greg Willis from Denver, CO, usa · CC BY-SA 2.0

Over 10,000 square metres across two chambers, the second a single vast hall. Named by the survey party that walked into it.

Sources (1)

Ha Long Bay Management Board