One small note - Czech Republic still allows for anonymous SIM cards. You can walk into any tobacco shop, pay around 4€ and get a pre-paid SIM which can be charged in cash.
Summer and Technical students (or basically anyone with a CERN account) already have access to much more detailed maps, if they care to search around CERN's GIS portal a bit.
Additionally, those who know the right people can get a paper version of the galleries map with all the interesting spots (unlocked entrances, light switches and spots like "zombie cages" or "connor's death") marked.