Regarder means "to look at".

Je regarde la maison. -- I look at the house.
Je regarde de belles collines. -- I look at beautiful hills.

It isn't "de" that means "at". The "at" is part of the verb "regarder".

But, strictly speaking, the sentence:

Je regarde des collines is ambiguous. It can mean "I look at hills" as well as "I look from hills".