In the MAIN Lowerdark section very close to the transition to the Chazbash section, there is a placeable indicating that there is a narrow passage above the cliffs. However, climbing using the Climbing Tool in the crafting menu does not move the PC, in this case, Kepli Underbough, to the intended location. He was just moved a single pace left of his current position on the same z-level. Probably an oversight.
That is actually just to represent a hole you pop out of if you use one of the alternate entrances to the Lowerdark (I think.)
Then it should allow you to return the same way in the least. Just like how Frodo and company scaled the heights near Minas Morgul, they should be able to climb the other direction.
Gravity works in one direction. It's much easier to go down than it is to go up.
Allow me to quote the transition.
Quote[A passageway here is narrow and cramped, but let you get free to another portion of the Lowerdark, if indeed you can squeeze through without bashing your head...]
The message sounds like the transition is supposed to work, at least from the MAIN Lowerdark section.
When you go through the other way it's made very clear its a one way trip.
It looks like they just reused the description for the exterior hole.
I still haven't found the area you refer to or it's location, but sounds to me there isn't a bug in place. If you want me to check it next time I open toolset, just give me the area name precisely and as easy and simple found location as you can. Avoid putting names or describing places that others would not know about or could find out IG. In such case, just put it in exploitable bug section if anything.
I think I found it. Should be fixed for next reset.