Go through the gate leading to Valravn. Follow the path and go slightly right. In the damaged tower you will see another Lorestone. Go through the gate until you reach a stone door with the Valravn symbol on it. You will be warned not to trust your eyes, or the illusion of the enemy will soon end the journey.
Go up through the path and push the bridge. Then approach the oval portal. Go through it and your reality will become distorted - here's one of key mechanics in Valravn's realm: every time you enter such a portal, the world around you will be altered (most of the times the changes are noticeable right after crossing the gate); some objects may be moved or can disappear altogether, revealing a new path, etc.
In this case, the gate will disappear and you will be able to proceed with your journey. Run on, enter the tower and take the ladder up. Approach the big gate and open it. When you approach the next door, more enemies will appear. This fight should not be problematic.
Go further and find the gate with Valravn's symbol. You have to find and recreate that symbol in the environment. Take the portal right next to you and you will reveal a passage via the stone wall. Go up and you will reach three symbols on ropes. Your task is to combine them into one, which will open the way further.