There are at least three different secret tunnels, one for each Wall. The tunnels are connected to some place/places outside the walls where people or titan shifters live.


1) Eren’s father, Grisha, was a titan shifter. He definetely knew something about titans and the walls since he knew about Rod and his family’s powers. Hannes told us that “there was this epidemic disease in Shiganshina, but one day doctor Jeager came carrying the medicine that saved everyone”.

I doubt Grisha created the medicine by himself, I believe he went outside, using this tunnel, and got the medicine from the “Outer world” (whatever there is outside the wall, a village or something).
Where’s the entrance of the tunnel of Wall Maria? Of course in the basement of Eren’s house.
Grisha used it to get the medicine, he wanted to tell Eren about it as soon as Eren said he wanted to join the Survey Corps to get outside of the walls and to kill titans.

The key he gave him opens the entrance of this tunnel.

2) Where’s the second tunnel, the one of Wall Rose? Of course under the castle of Utgard!
In chapter 38, the Survey Corps get to this castle to rest. They immediately notice something weird. It looks like the castle had been a shelter for some kind of “smugglers” who brought inside the castle lots of weird foods and drinks.

There is this bottle of wine. On its label there are words written in a language that the Survey Corps can’t read. And there’s canned food, again written in some weird language that doesn’t belong to the walled world…but that Ymir understands.

This means this food and wine aren’t from the walled world, but from the world outside the walls, probably from the same place where Ymir used to live.
How did it get inside the walls?
Reiner says this while searching for titans inside the castle

this means for me that in the dungeons of the Castle of Utgard there’s the second tunnel that somebody used to get food and drinks from outside. Who is the one who knows about this tunnel and used this castle as a shelter? Probably another titan shifter, probably the one who transforms into the Ape Titan. That’s why he tried to kill off all of those who were there, to prevent the Survey Corps from discovering the entrance of the tunnel.

3) Where’s the third tunnel, the one in Wall Sina? I’m not so sure about this.
The fake king here has near him the same bottle of wine the Survey found in Utgard. This means the king is drinking a wine that comes from outside the Walls.

I believe whoever gave this wine to the fake king, got it using the secret tunnel located inside Wall Sina. The entrance could be in the underground city, inside the mansions of one of the nobles, or of one of the people of the Wall Cult, or maybe inside Rod Reiss’ mansion or inside the huge cave where Rod Reiss turned himself into a titan.
How did Rod Reiss get all of those bottles with titans’ serum? What if he, or someone for him, went outside to get them?


Greek Mythology Meme | Five Titans [ 3 / 5 ]

Atlas: the Titan god of endurance and astronomy, he was the first to teach mankind astronomical science; one of four children by Iapetus; he sided with the Titans during the war with the Olympians, and was sentenced by Zeus to replace the original four pillars in holding the heavens and earth apart; one account tells that he later met with Perseus, who turned him to stone using Medusa’s head, and he was relieved of his burden at last