Accessed through a vent in the Furnace Hall, the Supervisor's Office of the Vale Street Ironworks is where the Thief-Taker General stashes Cornelius' Ring inside a large Watch Strongbox. Garrett must solve the relatively-simple puzzle--which reveals the Watch emblem--in order to retrieve the ring.
Upon doing so, however, the Thief-Taker General returns, forcing Garrett to flee the foundry through the only other door in the office, which leads outside into the Inner Yard.