a stronghold: a high, hard-to-reach place that people hold or hide in because the ground itself protects them
This word names a place, not a feeling. The hill country of Israel, Moab and Judah is full of cliffs, crags and caves, and anyone who climbs into one of them is simply hard to get at. That physical fact is the whole idea: the strength belongs to the ground rather than to anything a builder put there.
Two kinds of people end up in such places. The hunted go because nowhere else is safe. Israel hides from Midianite raiders in the dens and caves and strongholds of the hills, and David, tracked by Saul, keeps to the strongholds of the Ziph wilderness and later of En Gedi, with fighting men from Gad, Benjamin and Judah coming out to join him there. Armies go because a height is worth holding. Moab's strongholds are seized in one of Jeremiah's oracles, Babylon's soldiers give up fighting and sit in theirs, and when Chronicles says David lived in "the stronghold" and that the place was therefore called the city of David, it means the rocky citadel he had just captured.
The safety such a place gives is real but never absolute, and the prophets press on exactly that point. Ezekiel warns that plague will find the people who are in the strongholds and the caves. Jeremiah's Babylonians sit in theirs with their courage drained away. Isaiah alone turns the picture into a promise: the person who lives honestly will live high up, with "the rock strongholds" for a refuge, bread given and water sure.
A longer relative, metsudah (מְצוּדָה), covers much of the same ground, but it also means a hunter's net and it is the word that calls God a fortress. This shorter word does neither. Every one of its eleven appearances is a real place on the map.