Stronghold

Stronghold was a term used to indicate a well protected structure.

Vulcans's T'Karath Sanctuary was a stronghold during a Vulcan civil war. 

Elim Garak once called Deep Space 9 "a stronghold of his people's most hated enemies". 

In late 2371, the former members of the Shakaar resistance cell headed to a stronghold on Kola Mountain.