Agencies that organize tours to Halong Bay and Cat Ba Island offer the possibility to take part in a trekking. They gave me two options, the short trek and the long trek. I chose the short trek, 3 miles (the long trek was 8 miles). It was a nice experience climbing the mountain.
The island of Cat Ba is of bio diversity conservation significance due to the endemic and endangered species that inhabit its forests and its shores. One of them is the Golden-headed languor, one the most endangered primates in the world. Other unique species are the Green and the Hawksbill turtles, the seahorses, and several land snail species. Many of the plants found throughout the island are also of scientific importance. Nowadays Cat Ba's National Park is a top tourist destination.