The Hidden Blade Assassin's Creed in Depth

Assassins are forbidden from using weapons inside their fortress with the exception of the training circle. The third tenet of the creed is to protect the Brotherhood, so Altaïr is not allowed into the fortress when Exposed or Unseen. Unless...

The trick is to become Exposed outside of Masyaf Village. There are two guards at the village gate that the game considers to be in The Kingdom. Pick a fight with one of them.

Dash through Masyaf Village to the fortress. You want to be Unseen or Exposed when you reach the door. If you Sprint too efficiently, it's possible to lose your pursuers and become Anonymous. That's why I jog part of the way through town.

Once inside the fortress, you can use weapons as long as you remain Unseen or Exposed. Once you Vanish it's all over.

The Fortress guards will not defend themselves. However, your pursuers from the Village will follow Altaïr into the Fortress looking for a fight. The "safe" thing to do is to leave at least one of them alive. As long as he's in Open Conflict, you're Exposed and can continue to use weapons. He will follow you around and pester you.

If you want to be left alone for your killing spree try this: Kill the Village guards right next to the training circle in full view of the Instructor and his students in the ring. Apparently they qualify as enemies and this will sometimes keep your status as Exposed even after all the guards in Open Conflict are dead. This doesn't always work for me.

Important: This video was shot by Replaying Memory Block 5 from a finished savegame (no penalty for killing civilians). According to Jami-bunny, the glitch only occurs in Memory Blocks 5 and 6. I can confirm that it didn't work halfway through MB5, after assassinating Jubair al Hakim and returning to Masyaf through the Kingdom. I was hoping to catch Al Mualim in his office and use weapons against him. Instead, I got the blue memory wall at the entrance to the fortress. It may be the fact that I entered Masyaf from the Kingdom. The best time to try this glitch is immediately after speaking to Al Mualim at the beginning of MB5 or MB6.

Finally, there's sometimes another glitch when using the Hidden Blade inside the fortress where several line segments (about the size of the blade itself) hover in mid-air following an assassination. I've witnessed it myself but didn't get it recorded.