Hang Hanh is one of the longest grottoes in Ha Long Bay, lying 9 km west of Cẩm Phả Town and 20 km from Băi Cháy Beach. It is 1,300 m long, and stretches throughout the stone mountain of Quang Hanh.

Hanh Grotto is extremely beautiful. The small boat will take you through the stone passageway by lamp-light, casting magical colours on the hanging stalactites.

The French named it “Le Tunnel” or Tunnel Grotto. The mouth of the grotto is so low one has to go by small boat to pass through.

To get there, tourists can hire canoes in Đoan wharf (Ḥn Gai, Hạ Long City) or take a coach to Cẩm Phả. At the Cẩm Phả wharf, one can also hire boats or canoes to go to the grotto. One should visit the grotto at low tide, as this is the time the mouth of the grotto appears. Remember to bring along torches before starting the journey. It takes one some 60 to 90 minutes to complete the trip. Hang Hanh Grotto seems suitable for adventures. Another matter of no less important is that the boatmen must be experienced or else you will get locked up in this deep “Water Palace”.

In front of the present-day mouth stands Ba Cô (Three Girls) shrine in a towering piece of stone. Legend has it that: “Once upon a time there were three girls who often went to the sea together. One day, they caught a pouring rain and took shelter in a grotto. They found the scenery so captivating that they forgot the time of rising tide. Locked up in the grotto, they passed away and became Water God.”

Today, fishermen usually went to the shrine to pray for their bestowing favours on them.