After finishing all four bosses head towards the temple.
The first attraction is to cover a very long path without making a mistake which means you have to use all the powers you possess.
After getting to this place you will learn that Elika's father has been completely possessed by evil powers. Fight him. Ahriman appears after the fight. Since that moment you will observe the world from his perspective. Run onto the wall on the right.
Don't stop even for a moment. Go right all the time. The exemptions are shining points. You have to stop exactly in front of them and wait until the wave of slime falls down. Then go further.
You will have to heal three locations on your way. It will weaken the beasts a little every time.
At the end you will reach one red ring. Jump onto it and then to the other ones. Be careful because you will have to press Quick Time Events key.
Elika will push you in the direction of a tree in the middle by using all the powers she has left. Then she falls on the ground. Take her outside...
...and put her onto the altar situated in front of the door. Now head towards the desert and cut down four trees situated on small buildings.
Go back to the temple and here cut down the last fifth tree. As a result you will obtain the 1001st Light Seed.
Take Light Seeds to the altar. Now the only thing you can do is to watch the ending of the game.