In the southwest of Uganda, along the boundary with the Democratic Republic of the Congo (DRC, or Zaire), lies the Bwindi Impenetrable National Park. Covering an area of 331 square kilometers, this park is one of the largest natural forests in East Africa. It also has a large and varied ecosystem that includes about 120 species of mammals, 346 species of birds, 202 species of butterflies, and 163 species of trees. Visitors to the park can take a variety of guided walks - to the wildlife, to waterfalls and even to a number of peaks in the park. But the most popular activity is tracking down and trying to view the rare mountain gorillas. The park is home to about half of the world's Mountain Gorillas - the other half being located in DRC (Zaire) and Rwanda. While tracking down gorillas, the trackers and their guides follow signs - pressed down grass, droppings, broken branches and twigs - that would suggest the gorilla's previous locations. Gradually, the trackers get closer and closer to the animals until they are found. There are strict rules to prevent any disturbance to the 300 odd gorillas that survive in the park. Since even the common cold could prove to be very dangerous to the gorillas, no sick visitors are allowed to get close to the animals. Other than the gorillas, visitors can watch the chimpanzees or catch a glimpse of the incredibly varied birdlife and butterflies.