Approach the ravine in Lavasturm that leads to the entry to Jungfernschlucht and speak to Sebir der Historiker ( -167.86, -9.63, -546.37 ) /waypoint -167.86, -9.63, -546.37 who tells you about the sage who needs to be rescued.
Once you've started the quest with the Sage, travel to the bottom of Soluseks Auge (sublevel 6, where translucent paths wind over the lava) and enter Nagafens Unterschlupf. ( -202, -617, -198 ) /waypoint -202, -617, -198.
Note:To get to Nagafen's Lair you will need to take a lift ( -325, -595, 187 ) /waypoint -325, -595, 187 to the third floor in the Giant Apartments, but it may appear that you can only travel up to the second floor. To get to the third floor, open the door once you arrive at the second floor and hit the "up" option on the triangular button just inside the door (you may need to run into the room and back to the lift, but there is a short delay on the lift which should allow you to do so before the lift moves up to the third floor). There will be a one-way ledge at ( -103, -614, -292 ) /waypoint -103, -614, -292 followed by the Oratorium von Thyr. This instance is not required for the quest, but must be completed unless you have the assistance of someone with access to the deserted version.
Speak to Haushofmeister Inferinus who tells you that you need to learn the Elder Dragon language to be able to speak with Lord Nagafen.
Return to Wissender der Zeitalter in Antonica on the top floor of the Orakelturm. If he disappears or is not there, leave and re-enter the tower again. He tells you that you need to find 26 translated runes of Elder Dragon to learn the language.
On a bookshelf across from the door. ( -127, -32, -140 ) /waypoint -127, -32, -140 (You get access by clicking on a grate in the floor at ( 5, -26, -121 ) /waypoint 5, -26, -121 on the second level down in Stormhold.)
Runes #1 & #2: You will have to complete the access quest Den Schöpfer herbeirufen in order to unlock the door leading to the lower levels.
Rune #3: You will either have to complete the access quest Eingang zum Obelisken or use the Feerrott zone-in which puts you just inside the Obelisk.