Ptarmigan Tunnel in West Glacier, Montana

Forged in 1930, the Ptarmigan Tunnel in picturesque Glacier National Park was created to allow horses and tourists a better view of the surrounding natural wonder, and now the thoroughfare remains like the entrance to some underground kingdom. 

The nearly 200 foot long tunnel was created by a pair of steel jackhammers that pounded away at either side of the tunnel until they nearly kissed in the middle. To avoid a potential romantic (if catastrophic) collision, the process was helped along by dynamite blasting that simply brute forced its way through the rock. Once complete the tunnel led right through a natural barrier known as the Ptarmigan Wall. The interior of the passage is unadorned with the craggy rocks walls exposed all around.

In 1975, sharply-angled steel doors were installed at both ends of the path, giving the tourist tunnel a surprisingly fortress-like feel. Despite the added defenses, the tunnel is still a popular feature among the Glacier hiking trails and its doors are open most of the year.