Complex sentence: Floorball is played indoors on a rink, the size whereof can officially vary from 18--22 meters wide to 36--44 meters long, and which is surrounded by 50 cm high enclosed boards with rounded corners.
Split into simpler sentences: Floorball is played indoors on a rink whose size can officially vary from 18--22 meters wide to 36--44 meters long. The rink is surrounded by 50 cm high enclosed boards with rounded corners.