Ce n´est pas un mitho, je suis allé vérifier moi-même. Par contre j´ai oublié de dire qu´il faut surtout sauvegarder avant de sauter, on ne peut plus remonter
Hidden Area
You can find this area if your Acrobatics skill is high enough (I did it with Acrobatics at 87 but it might be possible with a lower level - anyone who does it, update this with the minimum you needed). And for your sake, SAVE FIRST! You may die along the way and you can NOT return to the normal area after you get there anyway.
During the Vaermina Daedric Quest you will enter Arkved´s Tower and eventually reach Arkved´s Lost Halls. When you get to a big room with a bunch of trees in it, don´t go up the stairs on the right but go straight ahead and through the next two doors. You will end up back out in Arkved´s Oasis. Turn left and you will see a tiny ledge that wraps around the corner - Jump over to it and follow it around. From there climb up the slope and look downto see the hidden area. Not much to look at from here so walk on top of the outside wall of the tower counter-clockwise until it dips down to its lowest point and hop down. If you hug the wall as you fall, you´ll land on a tiny ledge so it´s not as big a fall as it looked from above. Drop down again to the floor and hop up onto the little ledge that´s a foot above the floor. Follow the ledge across to the side with the stairs and make your way down. When you get to the bottom you will see the support columns for the tower are floating above the ground. Okay, could just be the freaky nature of this realm, but check out the spot where the stairs begin.
Comment: I was able to do this almost at the beginning of the game. My acrobatics couldn´t have been higher than 26-28 at the time. If you´re not wearing any armor or carrying much gear, all you have to do is make it to the small outcropping so you can walk around. Judging from the way the pillars and stairs in the bottom of the tower are arranged, it´s safe to say the developers didn´t intend for the player to be able to get inside this structure. There´s also a door there that has no effect. I had to use the no clipping console cheat to get out.
Comment 2: In order to escape the "secret area" move to the second floor of the fortress. Go out one of the outside facing doors that lead to a floor with short walls and no ceiling (kinda like a patio), use a shield spell then jump down to the ground below outside the castle. Using the walls to help break your fall, move to the front outside part of the fortress to find a door, the door leads to the room with the really big funiture, allowing you to ocmpletely bypass teh atronarchs in the hallway.