This is probably the most visually stunning climbing structure on our list. Stretching more than 120 feet into the Dutch sky, the vaguely S-shaped Excalibur tower has sections that are past vertical (meaning that climbers have to negotiate overhangs that have angles of more than 90 degrees). The centerpiece of the Bjoeks Climbing Center in Groningen, this outdoor wall is certainly a challenge for serious climbers. However, the towering structure has routes on both sides, so gentler climbs can be found on the face that is directly opposite the severe overhangs. There are smaller climbing walls at the Bjoeks facility, so novices can cut their teeth before attempting the 120-foot giant.