From GE-Korea's [GM TIP] 오쿨타 요새 리뉴얼, Occulta Fortress will be revised in v5.x. See [V3.0 Feature] Occulta Fortress and Arconis' sGE Secrets for comparison with the current version. A question mark (?) denotes confirmation needed due to uncertainty from sloppy translation.
You can enter Occulta Fortress from Errac Tierra Dias or Noche (E9/F9). It seems like no Ancient Rune is needed to enter anymore. (In v4.5.0, entry cost was reduced from 5 to 3 runes.)
Inside Occulta Fortress, the traps in Room of Mechanic (G6) have been removed. You can move to the secret area from the green arrow (E6). Notice that the screenshots did not include Nar, so perhaps he is no longer necessary to open the way.
Use Ancient Runes - An, Ar, Ti, and Te (1 each) to summon Kobold General, which can drop Recipe - Elite Le Blanc (low drop rate) and Ancient Rune - Ar.
Once the Kobold General is dead, you can move to the next area. Use the Key [Occulta, General's Room] to enter the room (F3/G3). All monsters in Occulta Fortress can drop this key (low rate).
In the General's Room, there are 2 dials. The left dial allows you to summon Kobold General with Ancient Runes - Ar, An, Ti, and Te. The summoned Kobold General has higher chance to drop Recipe - Elite Le Blanc and 100% chance to drop runes (?).
The front dial is to access Mufasa. It requires consumption of Ancient Runes or something (?).