The Cold Regions Research and Engineering Laboratory (CRREL) Permafrost Tunnel is a research facility carved into a hillside of permanently frozen ground about 16 miles north of Fairbanks. The U.S. Army Corps of Engineers excavated the tunnel in the 1960s to study permafrost behavior, and it has been in continuous use as a research site ever since.
Visitors walk through a frozen corridor where the walls expose layers of ice, silt, and organic material deposited tens of thousands of years ago. You can see intact root systems, ancient grass, and occasionally bones from Pleistocene megafauna. The temperature inside stays at about -3°C year-round, so bring a jacket even in summer. Tours are available in summer months and must be arranged in advance — the tunnel is an active research facility, not a commercial attraction. Check with the University of Alaska Fairbanks for current tour schedules.