Probably one of the must sees in Panama is Macho de Monte.  It is located about 12 kilometers south of Volcán at the tiny community of Cuesta del Piedra. Go downhill, the turn is unmarked and will be on the left. The road to Macho de Monte is in between Restaurante El Porvenir and Mini Super Meinor.

Less than 3 kilometers, past the guardhouse for the hydroelectric plant and cross two bridges.  Park your vehicle by the ranch on the right.
 
There is a path near the guardhouse that leads down to the river. Ask the guard to point it out.

Here's an exceptional video with spectacular footage.