Ahh. I knew about "estar" but I never knew that about "ser". Very good to know!

This little nugget would have come in handy when I was learning Spanish

And then locations and buildings come to fuck up that way of remembering it, because la biblioteca está allí, not la biblioteca es allí.

True that. I guess maybe it's because a building's location isn't necessarily part of its essence. Or how it feels more natural with respect to a person, e.g.: "yo estoy en la biblioteca" makes sense cause a person moves from place to place. I guess technically buildings can be moved but it's still a bit confusing.

The library is a thing, not a person. That's why you say está, because there's nothing inherent about a library, it's just an outer description. In general location descriptions are described with está, no ser.

Estoy triste: I am sad right now Soy triste: I am a sad person, in general.

La biblioteca está genial: the library is awesome right now (maybe due to an event or special decoration or because it was recently cleaned).
La biblioteca es genial: the library is awesome in general.

Tengo hambre: I am hungry
Soy hambre: I am hunger/(a hungry person)

Don't know, both would be ok, depeding on context.

• Dónde está la biblioteca?
• es aquí

Is totally fine, except if you are in a complex of buildings, or something like a mall or refering to the city (or similar) where the library is, then «está aquí» is the correct one.

Same in spanish, but we tent to use the "i have" way more, the other implies that you are reeeeaaaallyy hungry