Dug by the military in the 1960s, this passage was intended to test methods of tunnel construction in permafrost, a layer of soil below ground which never naturally thaws. Tunneling introduces new sources of heat and airflow to this geology, causing potentially dangerous thawing and collapse. These effects needed to be studied to design safe tunnel and bunker building methods in interior Alaska. The tunnel was turned over the the University after the military had finished, and was then used as a geology experimentation site and archeological dig to study fossils preserved inside the permafrost layer. The tunnel is kept ventilated in winter and refrigerated in summer to maintain the internal temperature and prevent cave-ins.

Note: this was an "official" visit along with a freind's geology class. The teacher didn't mind me poking around the more interesting parts, although I did get some funny looks when I pulled out my own hardhat and headlamp.

The refrigeration unit covering the entrance to the tunnel.

Just inside, with some ice stalagmites (or upside down icicles) under the cooling unit.

Inside the tunnel, halfway back there is a downward sloping side passage to bedrock.

A large "Ice Wedge" with some wierd mold growing on it that NASA is investigating.

Despite refrigeration, the back end of the tunnel has started to collapse.

A website with some more info.

And another one.