Fort Knoxes are secure places where valuable items are kept. Synonyms for this phrase would be "safe havens," "strongholds," or "vaults." Such phrases describe or suggest a place that is difficult to breach, and only those with the correct clearance level can gain access. Other synonyms are "lockbox," "safety deposit box," or "treasure trove." All of these synonyms center around the idea of a location with a high level of security. The phrase "Fort Knoxes" is named after the United States Bullion Depository in Kentucky, which holds the majority of the country's gold reserve.