The Sarawak Chamber is located in Gunung Mulu National Park in Malaysia. And it is special as it is largest enclosed space in the earth. It remained widden until 1981 when 3 English people (Tony White, Andy Eavis and Dave Checkley) discovered it while exploring the underground network of caves in the park and found it. They traveled down miles into the passage and found many cascades and also an underground canal.
Facts about Sarawak chamber
Length: 700 meters
Width: 396 meters
and Dept:70 meters.
If you want to feel the massiveness, then I can tell you that it can easily accommodate 10 Boeing Jet Planes. It is also equivalent to 38 football field.
It is formed due to movement of Earth (a phenomenon known as uplift) which happened 5 million year ago and erosion of limestone by water flowing through the cracks. The high rainfall in surrounding rainforest also helped in creating this marvel.