[@A Lowly Wretch]

So would it be fine if the Lost Lands simply had a large number of hidden entrances? If you feel having too many entrances is overpowered, I could say that any entrance that is definitively known about destroys itself soon after. That they can only exist so long as they haven't been discovered, so to speak. A mortal wandering through without noticing wouldn't harm one, but being placed on a map would cause it to pretty much instantly implode.