Cave diving & Deer Cave at approx. 40 mins in the first 2 episodes, unfortunately no underground action in part 3, but some impressive volcanoes & canyons:
https://www.bbc.co.uk/iplayer/episode/m000cs03/earths-tropical-islands-series-1-1-madagascar

& on ITV3 at 9pm tonight Judi Dench visits Gomantong Cave in Borneo (& presumably on the Hub after that)...