Deadly Doorway
Doorways were made both to be aesthetically pleasing as well as helpful protectors. It wasn't unusual to have an entryway with a password required. Some of them also had traps to maneuver through. If you failed to pass the test, there was no guarantee that you would make it out alive...
Army Guessing Game
There were tons of obstacles against intruders throughout the grounds. Whether that meant an annoying door, a tricky walkway, a large lawn that allowed for an easy shot, or even a moat in some cases, there were a lot of ways to stop an unknown person from getting in. Quite a lot to get through...