For obtaining access to CERN site, you need to register for this event under "Registration" (menu on the left).
The workshop will take place at IdeaSquare (building 3179).
You can find an interactive google-map here: http://goo.gl/WNSa6P.
Please note: as the event takes place on a Saturday, CERN reception will be closed. Print your badge at home before the day of the event. Access to CERN site will be denied if you don't have it, or if you do not have a photo ID (e.g. passport) with you.
In case you forget to print the badge beforehand, as a last resort you can print it by inputing your code on the phone booth next to building 55, after which you will get the badge from the guards on the gate.