I was doing leviathan prestige run today and whilst waiting for more players to join discovered a hole in the one roof in the castellum that takes you outside the map and despite there being a turn back warning (it can easily be avoided by continuing forward), one can jump through this hole and following a specific path to what appears to be a corner of the royal baths that person can then jump around the corner (which I shot at in the above video) and glitch into the hallway leading to royal baths without the need to open the door through the castellum. Although royal baths wont be able to be activated unless it is the current challenge that calus has assigned it is still a very easy and fast way to maneuver through the outside map to skip both the underbelly or the castellum routes. Uploaded a video of this to youtube I apologize for the poor quality had to record on my phone as my computer is unable to run both destiny 2 and the recording software without crippling fps drops and even crashes.