Learn Hardcore Russian: Все заметили красоту старого здания. - Everyone noticed the beauty of the old building.

In Russian, все can mean either everyone or everything, depending on context. In this sentence, the verb заметили is plural and refers to people noticing something, so все is understood as everyone.

So:

Все заметили... = Everyone noticed...

If it meant everything, the rest of the sentence would normally make that clear from context.

Why is заметили used here, and what form is it?

Заметили is the past tense plural form of the verb заметить, which means to notice.

Breakdown:

заметить = to notice
заметил = he noticed
заметила = she noticed
заметило = it noticed
заметили = they noticed

Because все means everyone, Russian uses the plural verb form: заметили.

Also, заметить is a perfective verb, so it suggests a completed action: they noticed it.

Why is красоту and not красота?