Caves are plentiful in the Tongass, where scientists estimate there may be thousands on Prince of Wales Island alone. Around 650 have been inventoried in the Tongass National Forest since explorations began in 1987, and one reigns supreme: El Capitan. Thus far the largest known cave in all of Alaska, it has 13,000 feet (4,000 meters) of passageways, one of which is at least 12,300 years old. One can tour the cave with a Forest Service employee during the summer months, but be warned: The trail to the cave is strenuous and steep. Once inside, there are no trails or lighting so a flashlight is a must. Babies and children under seven are not allowed. Bring warm clothing; the constant temperature is 40ºF (4ºC).