You are asking a lot of "at/in" questions. When referring to locations, "in" is more specific than "at". "In" usually refers to a position inside the confines of the location. At can be used to refer to areas inside the confines of the location, but it can also refer to the entrance of the location or the general area outside the confines of the location. I'll meet you "at the pub" could be inside the pub, but it can also mean on the sidewalk/pavement near the pub. I'll meet you "in the pub" is inside the establishment. Prepositions are difficult and are often idiomatic rather than logical choices. But you have to start to make comparisons. It is not helpful to ask about every possible location.
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