Cerro Negro is a young, black-ash volcano about 19 kilometres from León, and it has become famous for a peculiar activity: volcano boarding. You hike 45 minutes up the steep slope, pulling a plywood or foam board, then sit on it and push off down the loose volcanic ash. Speeds can reach 80 km/h if you let yourself go, though most people brake more than they intend.
Tours depart from León every morning and are easy to arrange through any hostel or tour operator in the city. The hike up is strenuous in the heat — start early. The views from the rim are spectacular in themselves, and the volcanic landscape of black ash against blue sky is unlike anything else in the region. Bring goggles and a bandana to keep the ash out of your face on the way down.