The Guardhouse consists of a ground-level room and a cellar serving as the prison of Hjaalmarch. It contains two chests containing random loot. This guardhouse is not a picture of military order; The Jarl of Hjaalmarch had little need for an organized militia.
The Legion has attempted to improve the old guardhouse and the jail (which is more of a cellar with a single cell secured by an Adept lock), but it is still a mess. You can find a Heavy Armor Skill Book, 2920, vol 06 - Mid Year, hidden behind a basket and barrel near the bed.
- It is possible to become locked inside the Guardhouse if night falls while inside the prison, which is considered a separate location. Picking the lock to get back to Skyrim is considered a crime and has a 5 gold penalty.
- When doing the quest "A False Front" the dragonborn may become locked inside the guardhouse if night falls while in it. Do not pick the lock, as it is considered a crime. Just wait until morning for the door to unlock itself.