While Zion National Park

Getting to the subway does require some route-finding and rappelling, so it's not for the inexperienced

Only 80 permits are issued per day and they can be difficult to get during peak times in spring and summer.

While the subway itself is only a quarter of a mile long, getting there is a somewhat difficult 9.5-mile hike round trip

If you want to bring your friends you'll have to be selective; groups of more than 12 are not allowed.

Algae thrive in the low light deep in the subway tunnel, causing the vibrant greens seen in these

As swimming is required in some areas, going in the warmer months is advised.

The subway is located between two peaks named North and South Guardian Angels.

Heavy snow melts and spring runoff can flood and shut down the subway, so make sure you check the train schedule before heading out