I ran into a rift best cave that has invisible wall at its entrance and thus i cannot enter it.
Map shows there is path, there is nothing visibly blocking the way. You just cant go in through the clearly open entrance.
This has only happened to me once so I think it may be rare thing.
EDIT: I was just about to post this, but I was actually able to evade into the cave. I had tried this previously already, but it seems some correct angle let me enter. Im playing necromancer and my minions are all stuck outside. They cannot find a path inside.
So if you run into this, keep trying if you really want to get in. You might just succeed.