This is not the Gorlaeus building, it is the van Steenis building. Both are correctly marked in the base level, but the larger brown text (which the search function also seems to recognise as the "real" Gorlaeus Building) is in the wrong place, leading to misleading directions. 

Gorlaeus (Einsteinweg 55): https://www.universiteitleiden.nl/en/locations/gorlaeus-building#tab-1
van Steenis (Einsteinweg 2): https://www.universiteitleiden.nl/en/locations/van-steenis#tab-1