This unique site is currently at risk due to deforestation and mass tourism. The ritual natural sight involves millions of butterflies migrating every winter from Canada in search of better days. A splendid vision when the huge swarms fill the pine trees, brightening them with the colour of their wings. Follow the trails leading to the Sierra Chincua and El Rosario sanctuaries, the only ones open to the public, preferably during the week in order to avoid the crowds.