San Gil is Colombia's adventure town, a warm Santander base where the real draw is what you can do in the rivers, canyons, caves, and hills around it. The town itself is busy and workaday, but that almost helps: guides, buses, cheap food, and gear shops are close together, and most days begin with someone asking how wet, high, or muddy you want to get.
The classic San Gil day starts near Parque Natural El Gallineral, where tour companies cluster by the Fonce River. Rafting on the Fonce is the easy introduction, while the Suarez River is the more serious run. Nearby trips add waterfall rappelling at Cascada de Juan Curi, paragliding over the Chicamocha Canyon, caving, mountain biking, and bungee jumping.
This is not a polished colonial showpiece like Barichara. Come to San Gil because you want an active day in Santander's rough country, then use the evening for a simple meal around the main square and a bus plan for the next morning.