There are a LOT of unused doors in all the worlds. How about you pick one or two in each world and have them open into an empty house with a trap door or a door that leads to a short under ground tunnel. You could place a fight in the middle, but the idea is that it leads to a portal, ladder, door that takes you to another place.
One example would be: A desirable lower world location that is repeatable. You constantly send wizards down world on quests. It could be somewhat close but not at one of those. It should open into another house so that when you exit you are surprised at where you come out.
You should NOT advertise the update but leave them as a surprise, and put them on doors that people will not accidentally brush up against but have to seek out.
I thought of this while exploring one of the upper lofts in Avalon and thought one of those book cases ought to be a secret passage.
I think it would be better to not have a plot to this, and just have a couple of bosses in unadvertised houses for looting. They may have some loot to drop and their loot and difficulty may be adjusted by world. Their location would not be static, and would be changing every time and maybe player-specific?
