Con Coc Islet is located about 12 kilometers from Bai Chay tourist wharf in the southeast of Halong Bay. It is about 9 meters high above sea level and resembles a toad waiting for rain when viewed from a distance.

According to a Vietnamese legend, there was a time when the gods forgot to make rain, which caused a severe drought that threatened the lives of all living things. A brave toad led a group of animals to meet the gods and ask for rain. The toad was so successful that it was honored as the uncle of the gods.

From then on, when the toad ground its teeth, it would rain immediately. The sound of the toad grinding its teeth became a sign of rain and helped Vietnamese farmers forecast the weather for their crops.