It wasn’t until 2009 that the full extent of the cave became known, when a group of British cavers made the first survey of the cave. What they discovered was truly phenomenal. The cave is over 5.5 miles long with a river and some rooms big enough to fit a 40-story skyscraper. In one section of the cave, the roof has collapsed (probably more than a thousand years ago) to let in sunlight. There, the explorers found a pristine forest with all sorts of animals including monkeys and flying foxes.
If you are willing to pay around 3,000 dollars and trek through the jungle for days, a company has started trial tours. (tour link)