The mystery disappears once you treat the casino like any other venue with controlled entry. The practical difference is that ID, access restrictions and game schedules matter more than they do at a normal bar or restaurant.
Before leaving: remove the four avoidable failure points
Check accepted ID, dress code, the hours of the product you want and any admission charge. Those four details vary enough between Spanish casinos that a generic memory of “how casinos work” is not reliable.
At reception: expect controlled entry
Bring the original document the venue accepts and allow time for the check. Do not assume a phone photograph or driving licence will be accepted simply because it works elsewhere on the trip.
On the floor: you do not need to play immediately
Find the part of the venue you actually came for. If you are unfamiliar with a table game, watching first is reasonable. Ask staff about the table procedure and current minimums rather than guessing.
Phones and photos
Casino rules can be stricter than normal nightlife venues. Gran Madrid, for example, prohibits mobile-phone use at gaming tables and slot machines and prohibits photographs or video inside its premises. If you want to film or photograph, ask first.
The budget should exist before the first bet
Choose an entertainment amount you are comfortable losing and keep it separate from transport, food and admission. Do not increase it because the first part of the evening went badly. The point is to control the cost of the entertainment, not to recover it.
Plan the exit before the late hours become attractive
Many casinos stay open into the early morning. That does not mean the easiest metro or bus option will still be running at the same frequency. Know how you will get back before you start playing.
The three guides worth opening before a first visit
Verification sources
Primary sources used for the factual checks on this page.