An architectural challenge:
… The brief for the sports hall would not allow for windows on the sides of the buildings for reasons of privacy, safety and performance for the athletes. But a completely windowless gym would be dark and unpleasant, so NL Architects came up with a creative solution to filter natural daylight into the space. …
details and more photos on Inhabit – Tulip-Like Gymnastics Hall in Utrecht Provides Privacy But Maintains Natural Daylighting
Gymnastics Coaching.com 