In my primary school we had some poles in the shape of a right triangle (with one of the legs being formed by the ground) with different slopes, all of which were 5-6 metres tall. The slope of the steepest one was nearly 80 degrees. The ground was tiny pebbles/gravel which made small falls somewhat less of an issue. They served no purpose other than being climbed, it was built to explore one's boundaries and to be brave. Most of us were scared to climb them but some who were really good climbers had no problems and got instant street cred by doing that.