Rises

To remove the seal and access this tower you have to use Fanged Imp Ashes and let them hit at least once an enemy imp roaming around.

To remove the seal you need to wear Karolos Glintstone Crown or Olivinus Glintstone Crown and do Erudition gesture in front of the seal.

You can get to the tower via an invisible bridge starting on the other side of the ravine.

At some distance from the tower you will have to turn to an invisible spiral staircase on the left leading to a balcony above. The falling snow should show you the faintly visible right path.

Interact with the book on the pedestal. To remove the barrier blocking the entrance you must find three spectral turtles which you will find near the tower.

One is located in the bushes just behind the book pedestal to the left of the stairs. The other will appear on the road, just behind you. The last one is invisible because it hides in a small pond on the other side of the tower. Search for splashes on the water.