Already they knew Clearwater stretched for 140 miles and that some of the caverns were lined with turbulent rivers, while the Racer-Easter system contained chambers so enormous that a jetliner could fit easily within its walls with plenty of room to spare. In other words, the limestone underlying this region, beneath Malaysia's Gunung Mulu National Park, is riddled with some of the biggest holes, widest tunnels, and most mind-blowing voids anywhere on Earth.
If you are the kind of explorer who enjoys crawling down into wet, hot darkness in order to find more wet, hot darkness, Borneo is a dreamland, a Disneyland, and a Neverland, all in one.