To find the cache you have to play a whereigo cartridge. The cartridge can be downloaded here (username and password is the same as you use on www.geocaching.com). Special thanks to marcipanek for organising this cartridge.
This whereigo can be played anywhere. Literally anywhere. The physical cache is not far from the listed coordinates, which are at a building with southern constellations on the facade. The new North Terrace building is especially good at night.