When at the blocked off stairs, the player is told to stop and sit at one of the benches. Using an actor, an envelop containing a notepad, pen and a black-light flashlight is passed to the player. The player is then told to keep walking down the path before entering via a small side entrance.
See the benches? Stop and have a seat there. Someone will give you a package, do not look at him, do not speak to him....Good, the envelop will contain some tools that will be helpful for your assignment. Now keep going until you see the side entrance to the castle, that will give you a covert entry. Good luck.