Tiny state in Borneo, sandwiched between Sarawak and Sabah. After it was a big regional player a few hundred years back, Brunei became rich upon the discovery of Oil in the 1940s. For a period time the Sultan of Brunei was the richest person in the world.
The Gunung Mulu National Park in Borneo (near Miri) is a UNESCO World Heritage Site with caves and karst formations. The caves are home to over 5 million bats who exit the caves in search for food every evening in a spectacular way.