What type of sentence is this? "the dark windows stared out at the approaching storm."

(Generally) That's a declarative sentence.

(In Grammar) That's a complex sentence; it contains one independent clause and one dependent clause.

"The dark windows stared out at the approaching storm."

"The dark windows stared out." is an independent clause while "at the approaching storm" is dependent.

So it's a complex declarative sentence.

i claim you tobemy lord