Cavers in a squeeze. There are a few passages that require squeezing, like here. Some are too narrow to negotiate with a backpack. It's a good idea to carry 4 or 5 meter of rope and a couple of carabiners to lower bags down, especially if they contain heavy and fragile camera equipment.
Photo taken in the Clearwater cave system in Gunung Mulu National Park (Borneo)
The Clearwater System is believed to be the largest interconnected cave system in the world by volume and the 9th longest cave in the world at 189 Km (as of 2011).
For more photos, information and cave map, view my Clearwater cave photo series.