Castellfollit de la Roca is a municipality in the comarca of Garrotxa, in the province of Girona, Catalonia, Spain. The urban area is bordered by the confluence of the Fluvià and Toronell rivers, between which the town's basalt cliff rises. The town is in an area of less than a square kilometre, making it one of the smallest towns in Catalonia.
The basalt crag where the town is situated is over 50 m high and almost a kilometre long. It was formed by the overlaying of two lava flows.