Some 63 three-layer ETFE-cushions up to 26m long – a total area of 4500sqm – are mounted in this way. These cushions have to follow not only the curve of the arch trusses, but also the twist due to the different radii of adjacent arches. Cushions also form the façade at the eastern gable. In order to guarantee a tangential line for the rigid perimeter connections of the cushions at the nodes, the line of the springing and the crest to the swimming pool building follow a curve. The long building housing the sports facilities also makes use of lightweight ETFE-cushions so that a maximum amount of daylight reaches the climbing zone. In the centre of the green roof there is a rooflight in the shape of a trapezium on plan. Arched steel trusses with seven cushions span the 500sqm of this area. The structural steelwork rises higher in the middle, which results in a roof curving in two directions. The delicate construction gives the climbers underneath the impression that they are climbing under an open sky.