So, I've finished the castle, been a heck of a ride going through the ol' game. But I noticed there's two spots on my map that I haven't visited. A small bit around 12N2E, and a larger bit around 7N18E. I cannot for the life of me figure out how to get into either one.

The smaller one just doesn't have a door, nor any teleport leading in. The larger one actually has an entrance, but it's blocked by a teleporter that sends the party far away. There's no other path in. Phase Door and Apport don't work on this floor. It's been so long since I've played BT1, I can't even recall if I ever managed to get into these areas, or forgot they existed completely.

Anyone know if these areas are even reachable?

I can't find any inaccessible areas at first glance on the maps here
Maybe compare for yourself? I'm nowhere near Harkyn yet.

here

They haven't been reachable in the original either.