A secluded or unobtrusive building
considered safe for
use by secret agents
as a base of operations, as a refuge
or for a
. Archetypically, out in the middle of nowhere
, with generator
, and the like, it can sometimes simply be a city apartment that keeps a very
"Oh, the Smiths? You hardly see or hear them..."
Alternatively, a legendary night club/discotheque in Milwaukee, Wisconsin, behind a door marked "Universal Imports", and otherwise unmarked and NOT in the phone book...hmmmm....