The most confusing thing for me is that sometimes a portal is different going through one way than another.
For example, if you go to the 1st map, take the center portal, you end up at a crossroads. Go one left, and it takes you to Swamp Bog. However, go back through that same portal, and you're at a different crossroads (however, this last portal still leads to Swamp Bog).
Definitely worth marking down portal destinations in both directions if you're drawing a map, and don't assume Crossroads are the same just because they look like they are.
For example, if you go to the 1st map, take the center portal, you end up at a crossroads. Go one left, and it takes you to Swamp Bog. However, go back through that same portal, and you're at a different crossroads (however, this last portal still leads to Swamp Bog).
Definitely worth marking down portal destinations in both directions if you're drawing a map, and don't assume Crossroads are the same just because they look like they are.