When paratroopers are training to jump out of aircraft they jump from a static location - a building - and then slide down a long cable to the ground. The height of this structure is designed to be at a particular height where anybody who suffers from acrophobia [fear of heights] will be tested to the full. In the distance you will see 2 such structures that are used for paratrooper jumping.
In South Africa at the 1 Parachute Battalion in Bloemfontein this structure is affectionately known as the "aapkas" - monkey cage.
FTF goes to = Piet Retrievers