Learn Italian: Il portone del palazzo è sempre chiuso. - The main door of the building is always closed.

The base word is porta (door), which is feminine. When we add the augmentative suffix -one to mean 'big door' or 'main door', the new word portone becomes masculine. This is a common rule in Italian: noun alterations ending in the -one suffix are almost always masculine, even if the original word was feminine.

Does palazzo always mean 'palace'?

It can mean 'palace' in historical contexts, but in everyday modern Italian, palazzo is a false friend. It usually refers to a regular multi-story apartment building or office building. Here, il palazzo simply means 'the building'.

Why is it del palazzo instead of just di palazzo?

In Italian, when you say 'of the', you must combine the preposition di (of) with the definite article. Since palazzo is masculine and takes the article il, di and il merge to form the combined word del.

Why does chiuso end in -o here?

Chiuso (closed) is acting as an adjective describing il portone. Because portone is masculine and singular, chiuso must match it and end in -o. If we were talking about a regular door (la porta), it would change to match the feminine noun and become chiusa.