When I discussed with him to bring him along in the field, he had two things on his wishlist: Caving and rapelling down a moulin. We got both. Yesterday we rapelled in a roughly 20 m wide and 20 m deep moulin. Except that it was full of water. And we had a purpose: Water sampling. Now we just have to repeat it many times to get a time series and also install some loggers in that hole before the water drains out.