After you have given the Totem to one of the descendants of Tiber Septim you will be contacted by Nulfaga who tell you to come to Shedungent. When you speak with Nulfaga she will teleport you to Aetherius.

You will arrive in the floating island chamber, the first of the six chambers through which you must travel to reach the Mantellan heart.

Click on the statue next to you and a levitate spell will be cast on you, allowing you to levitate up to a tiny island on which there is a lever. Pull the lever and descend back to the first floating island. Now walk down the row of small floating islands, stand on the last one and pull the lever on the adjacent island. The island will descend, taking you to the second of the large floating islands. There are four doors floating over the island, and you only need to click on the south door. Now levitate down below the level of the second floating island and look for an opening to a room with a lever, enter and pull it. Now go back to the first large floating island and click on the statue again, levitate to the top of the chamber and look for the hole in the stars. There are two such openings, but there are blue bars on one of them; if you performed the preceeding steps properly the blue bars have been removed from one of them and this is the opening you will enter. Look for a floor lever at the end of one of the corridors and pull it. This removes a set of blue bars in a nearby corridor; now go down that corridor and pull each of three levers you come to. After pulling the third lever, go back and pull the first one again; now go back down the corridor, follow it (turn right, then right again) to the end where you will see another lever, which you must pull.

Now go back down to the first floating island and once again walk down the small floating islands. You will see an opening which was originally blocked by blue bars which you should now enter. Step on the carpet within and you will be transported to the next of the six chambers.