On the northeastern tip of the island, Viking Cave is a major collection point for outrageously valuable swifts' nests, the key components of the Chinese speciality bird's-nest soup. Nimble collectors scamper up fragile bamboo scaffolding to the roof of the cave to gather the nests. Before ascending, they pray and make offerings of tobacco, incense and liquor. Visitors are not allowed inside the cave, but most tour boats slow down for a good glimpse.
The cave gets its misleading moniker from the 400-year-old boat graffiti created by crews of passing Chinese fishing junks.