The way in. An entrance is the first thing a place says about itself.
Old French entrer, from Latin intrare (to enter), from intra (within); the verb narrowed in English to the specific opening or moment of crossing inward, and further specialised on the stage to an actor's first appearance.
The same word also names an actor's first step onto a stage, the moment a presence becomes visible rather than merely possible. A building's entrance carries that same weight: the one place a structure is caught introducing itself.