Usually will have a few cells inside often full with some young scrote serving out his sentence.
As a young Tom walking past the Guardroom is like running a Gauntlet, trying to get past without being shouted at for walking funny, having your shirt hanging out or other ill discipline issues! This gauntlet is magnified a 100 times when returning from a night on the pop. As long as you do not offer out the BOO and the rest of the duty staff (who are only watching everyone come home safe and not out to get you) at fisticuffs you should be ok.
One of the funniest tales I heard from a Guardroom was when a unit down south got a call from the local nightclub, "we have one of your toms here and he is legless". The BOO dispatched the Duty Driver and the Orderly Corporal at once who recovered the said individual. They could make no sense of his drunken words and his wallet was also missing so they threw him in the cells as identifying the poor chap was going to have to wait until morning. Come 0900hrs the RSM popped his head in the cell and gave it the "who the fuck are you" routine. The poor bloke started to panic asking where he was and who are you people. It turns out that he was not in the Army after all and just some visitor who got totally wankered in a squaddie nightclub. At least he got a free bed for the night with breakfast!