Here is a short video (30 seconds) of a hornet’s nest that Christy sent me from Seattle, WA. The video was shot on September 1st, this is the time of year when the nests are as large as they get.
Video of Bald Faced Hornet’s Nest
I have only seen hornets nesting in spacious places–outside, below eaves, or in open attics. In my experience, they do not live inside walls.