What's the greatest "single location" film?

[E.H. Ruddock]

I stand by Die Hard as a good answer.

[contamination]

Tape is another strong, underrated single location film. Like Bug, Tape is also based on a play.

Tape was the first movie that came to my mind when I read the thread title. Haven't seen it in ~20 years but I remember liking it.

[VinylGuy]

Tape is a very cool little movie yeah.

[Ms Harmless]

Pontypool

[tragabigzanda]

Whenever there's active promotion on the part of somebody else, whenever I see somebody all dolled up for a fancy photograph and someone's handing out flyers or whenever there's active promotion for something like that, as an imposition on my day, I hate all those people and I want them to fail. I have a visceral reaction to advertising and promotion. There's just something about salesmanship that grates on me on a very base level and I react very negatively towards it. I want those people to suffer and I want their enterprises to fail.

[spike]

Does Speed count?