Where is Damavand mountain?

I have read all the books. Now I have something bothering me. During the trial where Mountain fights Oberyn, how can Cersei choose Mountain as her champion. Mountain is not a kingsguard right?

• Answer:

  Spoilers for the fifth book, for clarification purposes. The way I've seen it explained is that when a member of the royal family is the accused, the Kingsguard is obligated to act as champion because it falls under the auspices of defending the family. An example of this is in the fifth book when Cersei opts for a trial by combat and will end up having Robert Strong, a Kingsguard (*cough*) defend her. But since Tyrion is the accused here, Cersei is not under obligation to have a Kingsguard represent her interests in the trial. And in fact, Gregor is a superior fighter to any Kingsguard at that time, especially with Jaime disabled. So while Cersei could have a Kingsguard fight in the trial, she doesn't have to and wouldn't really choose to if she could get Gregor to do it.