Where do I use key Perry gave me?

[The Black Dragon]

HELP I got the key from Perry the farmers son,but i can't figure out were to use it.

[Arokhs Twin]

It opens the Rynn sized door front entrance to the Sanguinade - the old ruins in the desert.

[The Black Dragon]

Where do I find these ruins[?]

[Arokhs Twin]

Fly over the mountain behind the gate. Be prepared though; the game gets very difficult from that part onwards.

[The Black Dragon]

Thanks I realy stuck.