(n.) A fastness; a fort or fortress; fortified place; a place of security.

acropolis asylum bastion beachhead bird sanctuary blockhouse bridgehead bulwark bunker castle citadel donjon fasthold fastness forest preserve fort fortification fortress game preserve game sanctuary garrison garrison house harbor harbor of refuge harborage haven hold keep martello martello tower mote motte peel peel tower pillbox port post preserve rath redoubt refuge safe haven safehold sanctuary snug harbor strong point tower tower of strength ward