Santuario Piedra Herrada is one of the wintering sites for the monarch butterfly migration, east of Valle de Bravo. In season, usually from late December into February, guides lead visitors up through the fir forest to the colony.
The butterflies are most active when the day is sunny and warm enough, so do not treat this as a guaranteed spectacle in cold or cloudy weather. When conditions are right, it is easily the strongest nature experience you can have from Valle.