I've completely finished the Thieves Guild quest line, which means I'm now Guild Master. Up until this point, I've had access to a very empty treasury. Now that I'm leader, I've noticed that the treasury has now been locked again and needs a key in order to be opened.
Is there a way to gain access to the treasury? If so, what kind of loot is hiding behind the locked door? In other words, is it worth breaking in?