Call ahead. Even if there not busy, if they know your coming they can prepare and you'll visit will be more enjoyable.
If you have a large party I believe they do like you to call ahead though. Just to give em a heads up. I know the A.G. one appreciates it. I've not actually made reservations. I prefer to eat in bar area where there's music. Just a preference.
Call them
If it's a part of 2 to 4 you don't have to. Just show up and you should get a table within a few minutes or as soon as you get there. They don't take reservations.
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