1. In Rune, go to Einhasad Temple (lower level) and speak to Priest Eliyah to get the quest. He'll tell you some gruesome stuff about human sacrifices in the Pagan Temple and asks if you really want to help him.
2. Once you agree, he explains Priest Flauron in Rune is in charge of finding human sacrifices! You'll need to find him to get a Sacrifice Mark, the onlything that will get you inside the Pagan Temple.
3. Priest Flauron is located in the upper most area of Einhasad Temple.
4. Priest Flauron will ask what you are doing there. Select "The Truth Beyond the Gate" from the quest list. Tell him you'd like to visit the temple.
5. He gives you the Visitor's Mark. Lucky you. You may now enter the Pagen Temple. The entrance to the temple is the opening behind Priest Flauron.