Da' Vane |
I think people are looking at Find the Path in the wrong way. Mechanically, this spell is like rolling extremely high on a Knowledge (geography), Knowledge (local), or Gather Information skill check, and should be treated as such.
It should therefore be able to find the sort of named locations that local inhabitants would know about, regardless of size. This means they could find landmarks, specific buildings, or even specific rooms in a dungeon - but only if they know the name.
You could ask any traveller how to get to the City, any inhabitant the location of the Queen's Arms are Hang Man's Rock, and any guard the location of the dungeon's cells. Ultimately, the spell is keyed to the location, not the objects - so while the spell will lead the the Liche's Treasure Vault, it will only lead them to where people think it would be, not to where the Liche actually keeps his treasure. If the Liche doesn't have a specified Treasure Vault, then the spell fails.
The spell should only give the shortest route, regardless of guardians and traps. It should not reveal any traps. It probably shouldn't reveal any secret doors - although if the spell leads into a dead-end and hints that the location lies beyond it, then there is probably a secret door there somewhere. The most it would do is highlight the wall the secret door is on.
Ultimately, the advice for handling divinations is important here. The spell makes finding a location easier, but that is rarely the entire adventure. Just as with identifying a villain with divinations doesn't neccessarily ruin an adventure - they still have to catch them. This is the very thing that the DMG advises against - denying the players abilities for the sake of an adventure.