Today, hundreds of climbers scale the sheer rock walls of Devils Tower each summer. The most common route is the Durrance Route, which was the second free route established in 1938. There are many established and documented climbing routes covering every side of the tower, ascending the various vertical cracks and columns of the rock. The difficulty of these routes range from relatively easy to some of the most challenging in the world. All climbers are required to register with a park ranger before and after attempting a climb. No overnight camping at the summit is allowed; climbers return to base on the same day they ascend.