Rio Claro is a small rainforest nature reserve 3 hours from Medellin, 5 hours from Bogota (it's on the road between the two). This video doesn't really do the destination justice - the river is usually much more crystalline - but this is the best we could find.
Activities and tours at Rio Claro include canopy zipline tours, fishing, caving, hiking, birdwatching, rafting and kayaking.
Rio Claro Photos:
Rio Claro - bathing in the river surrounded by Colombia's rainforest.
View from rooms in Rio Claro Cabanas.
Explore caves in Colombia - hike through the rainforest to the cave entrance.