Ha Long Bay is split in two by a wide channel running north-south: the larger, western portion contains the most dramatic scenery and best caves, while to the east lies an attractive area of smaller islands, known as Bai Tu Long. Before exploring the caves, you need to buy an entrance ticket ($1) from the Bai Chay boat station. This allows entrance to a maximum of five caves and includes a coracle to ferry you from your main boat. The bay's most famous cave is the closest to Bai Chay: Hang Dau Go ("Grotto of the Wooden Stakes") is where General Tran Hung Dao amassed hundreds of stakes deep inside the cave's largest chamber prior to the Bach Dang River battle of 1288. The same island also boasts the beautiful Hang Thien Cung cave, whose rectangular chamber, 250m long and 20m high, holds a textbook display of sparkling stalactites and stalagmites. Continuing south, you should single out Ho Dong Tien ("Grotto of the Fairy Lake") and the enchanting Dong Me Cung ("Grotto of the Labyrinth").

Of the far-flung sights, Hang Hanh is one of the more adventurous day-trips from Bai Chay: the tide must be exactly right (at half-tide) to allow a coracle ($10 extra) access to the two-kilometre-long tunnel-cave; a powerful torch is very useful. Dau Bo Island, on the southeastern edge of Ha Long Bay, encloses Ho Ba Ham ("Three Tunnel Lake"), a shallow lagoon wrapped round with limestone walls and connected to the sea by three low-ceilinged tunnels that are only navigable by sampan at low tide. This cave is sometimes included in two-day excursions out of Bai Chay but is easiest to arrange from Cat Ba .