Honestly I also quite lost on what fortress he is referring to. If you do progress according, you should learn that those teleporting device are made by the old dragon knight orobas, for the easier to travel around orabas fjords. But after the betrayer incident, slayers had take down most of the devices, hence majority you found is not active, which has nothing to do with the teleporting device in broken valley. But still there are few which still active, but it wont teleport you to any fortresses, just other location in fjords only.
