5/5 - Excellent
CERN open days were excellent. Next one in 5 years (2024?). Book early to get LHC fasttrack to avoid 2 hour queues, or (reportedly), go to CMS. Catering at Meyrin good, but suggest take your own to ALICE. Buy TPG transport card and load in advance if you don't have a guaranteed-accepted contactless debit or credit card to travel around. Free transport between between CERN sites were available and generally if you stay in a Geneva hotel.