The CERN Scuba Club is located at the barracks next to the CERN Meyrin Site. To be more precise, it is located in the first Barrack (Building 564) using the middle entrance. There are a limited amount of free parking spots available which do not need a CERN access card.
For getting to the barracks, please have a look at the official CERN Webpage on how to get to the Meyrin Site: https://home.cern/directions
Or directly for the navigation system:
Route de Meyrin 375
1217 Meyrin
Switzerland