From Longman Dictionary of Contemporary Englishguardroomguard‧room /ˈɡɑːd-rʊm, -ruːm $ ˈɡɑːrd-/ noun [countable] TBa room for soldiers who are guarding a military camp
Examples from the Corpus
guardroom• Under the vaulted ground floor was a guardroom and small prison.• The officers' quarters in the guardroom contained a large board labelled with the names of different areas.• At 1.15am, as they slept, Hobbins allegedly crept into the guardroom and took the rifle.• When he reached the guardroom he stopped and turned round for one last look at the parade ground.• As a final gesture they came upon the guardroom. 