Were is a past form of the verb to be. We're is a contraction of we are. Where refers to a place.
See also: Ware, Wear, and Where
We were lost in the middle of Timbuktu. No one knew where we were. Next time we travel, we're going to bring along a map.
(a) ______ going to Savannah for St. Patrick's Day.
(b) We don't know ______ we'll be staying.
(c) Last year we ______ forced to sleep in the van.