San Gil calls itself the adventure capital of Colombia and, unusually, means it. The Río Fonce runs through the middle of town at a forgiving Class II–III; the Río Suárez, half an hour away, is Class IV–V and serious.
Caving, paragliding and canyoning are all sold from the same handful of offices around the main square. Nothing much is priced online — you walk in, or you message.