Outside of Fairbanks, Alaska, there is a 360 foot / 107 meter tunnel bored into the permafrost.

The main tunnel was carved into a hillside by the Army in the mid-1960s to help the military figure out how to build roads and buildings on permafrost. Today, biology students from the University of Alaska make regular field trips - to walk back through time 40,000 years!

Jutting out from the frozen walls of the 40 year old tunnel are animal bones dating back many thousands of years to a distant past when saber-toothed tigers, mastodons and even camels roamed Alaska's interior.

Just inside the entrance is a spectacular fossil that has been locked into the frozen wall for 14,000 years - the tooth-filled jaw and bones of an extinct long-haired steppe bison.

But the unique sights come with a down-side - the smell! There's a sour, musty stench that some have compared to opening an outhouse door. It's the smell of old plant and animal life that, after thousands of years, is now slowly and steadily decaying because of its exposure to the air.