One of my jobs at work is being the keeper of the keys. It takes four layers of keys to get into the keybox.
Security is a big deal. But as one friend noted, a crowbar is a pretty universal key. However, our work compound is protected by an electric fence with generator backup, a security guard and locked bar-doors in front of the locked doors.
Once you get into my office corridor, it takes only a skeleton key (or in England, it's called a mortice key) to enter my office. There are few varieties of those, so my actual office door is not very secure.