A nice place to be during a hangover. Generally characterized as having blankets hung over windows as curtains, dark-colored and/or eggcartoned walls, cool temperature, futons, couches, ceiling fans and several other low-key features that would otherwise go unloved.
Friend: (on phone) Hey, man! Wanna have breakfast at <bar name> with meh?
You: Nah, I'm all cozy in my hangover shelter...