I'm assuming, perhaps incorrectly, that the teleporter by the philosopher is the one I need to use to get to the fortress, but when I try to use it, it says it's inactive. I figured that was because I never got the password to the teleporters in Broken Valley, or because I needed to clear the depleated Mine first. I wasn't strong enough to clear the mine, so I've actually gone back and started the game again, because my character was too weak anyway, so the question doesn't apply so much now, although I'm curious as to what I did wrong.
What fortress are you trying to reach? One that is located in the cliffs, and surrounded by an Anti-Dragon Area? This is very near to the Broken Valley / Orobas Fjords entrance.
If this is the fortress you mean, there is another teleporter near high on top of one of the cliffs that look out to sea. Go as high as you can, and take a look at the cliffs between the fortress and the Grand Knight statue.
Do you have to unlock the special transporters in Broken Valley for the one in the fjords to work? Or have to finish the depleted mine--which is a problem until I can realign some mistakes I made in developing stats.
