NOTE -- You must not have Let Sleeping Dogs Lie activated. Also, if you have just finished that quest, you must zone before you can flag Making the Grade.
Talk to Fuepepe who tells you that the students' answer sheets from their recent written exams were stolen and that The School of Magic urgently requests that you track down the answer sheets and return them.
Continue through the tunnel section until you reach the Magic Door at (D-10).
Follow through to next crack, keep going until you see a Sealed portal at (H-9).
To open the door, you need a party of 3 mages, a WHM, a RDM, and a BLM. Or someone with a Portal Charm-permanent key item.
Obtain the Test Answers, which are dropped by Wendigos inside Inner Horutoto Ruins behind the Three Mage Door, or purchased off the Auction House under Other/Misc. The tunnels that lead to (H-7) look like dead ends, but keep walking and your character will be able to go through them. The room behind the tunnels is where you will find the Wendigos.