Surprise Cave is known as Sung Sot Cave or Amazing Cave. It is located on Bo Hon island. This is the most famous cave in Halong Bay.
The Surprise Cave was found by the French in 1901 and covers an area of 12,200 squared meters. The grotto has three chambers linked through narrow ravines. 

The first one  is similar to a theater hall with many stalactites hanging down from the high ceiling. A narrow passage leads to the second chamber, where a flow of natural light bathes the surfaces. The light is filtering in from above, through a large opening creating a natural skylight, this opening also serves as the exit from the cave. The deepest point of this chamber is a “royal garden”. It appears as a clear pond with fascinating landscape of small mountains. Many birds and plants are growing here. The mouth of Sung Sot Cave lies 25 meters above the sea level,  so from the wharf, you need to climb 50 steep stone stairs to reach it. When entering the cave, you will see that the cave is huge and that the distance between the ceiling and the ground varies consistently (30-2 meters). The high ceiling features numerous stalactites and the ground features many stalagmites all along the 500-meter paved passage. They have strange shapes formed through thousands years by the weather and the tectonics process. With the help of your tour guide, you can easily imagine lots of interesting characters hiding in the stone like a dragon, a woman or a big lion, etc. The walls and innumerable cracks and crevices are the evidence of the millions years of spectacular natural creation. Close to the exit, a mammoth formation stretches from the floor to the ceiling, tapering at the center to form a concave pillar that appears to be keeping the ceiling in place. Walking through the cave, ones imagination can run wild conjuring up all kinds of fantastic creatures and fanciful creations. On the side of the entrance, there is a stone in the shape of a horse and a long sword. According to the ancient legend, that horse and sword belong to Thanh Giong who defeated the An aggressors and helped the population chase away evil spirits and demons before flying back to heaven, He left his sword and horse to continue keeping the demons away.  Many marks of that violent battle still remain in the walls of the cave until now and the trail of his horse became many little lakes and smashed rocks. Sung Sot Cave is typical for karst caves in Halong bay and has extreme value in the field of geology, which is suitable for both of visiting and researching.