Learn Spanish (Spain): ¿Está lejos el museo?

We use está (from the verb estar) because we are talking about a physical location. Even though a building's location is permanent, Spanish always uses estar rather than ser to say where things are in the world.

Why is the word order está lejos el museo instead of el museo está lejos?

Spanish word order is much more flexible than English. In questions, it is very common to put the verb (está) first. You could also say ¿El museo está lejos? or ¿Está el museo lejos?, but putting the main idea (lejos) right after the verb sounds very natural to native speakers.

If we were asking about a feminine word, would lejos change to lejas?

No. The word lejos (far) is an adverb, which is a describing word that never changes its spelling to match masculine, feminine, singular, or plural words. It will always stay as lejos.

Why is there an upside-down question mark at the beginning?

In written Spanish, every question must start with an inverted question mark (¿) and end with a normal one (?). Because Spanish word order is so flexible, this punctuation helps the reader know immediately that a question has started.