This is after you get your battle tower DB, the whole valley is poisoned but you need to go back there in dragon form and clear out some towers, barriers and a general of 2.
The mine talked about is the alternate entrance with the key you get from mine guild guy in the mine towers by the mine the miners blew up. The mine guild guy that tries to fight level 27 black ring with his fists.
You can also land on Lovis' tower and mind read that doctor that had the tin foil hat for the password to his storage that is on one of the cliffs in there on the left hand side I believe.
That loony rhyming mage drops you there at one time if you keep messing around in the valley before it is poisoned.
