What can I do to eat in a grand hotel without acting like I'm going for the first time?

Go to that place, sit down, talk to the people you go with, and act natural.

When you want to go to the bathroom or receive service, ask the front desk. As long as you are polite and decent, it's not like going for the first time.

Of course, it depends on whether you want to hide it from your peers or hotels for the first time. If it is the latter, try to understand the hotel situation first and go to the front desk less. The latter can be blown at will, and the signature dishes will come back to blow when they are known at the front desk.