Heading out of Cassardis is required to reach the The Shadow Fort. If you have a Portcrystal close to the The Shadow Fort you can save a lot of traveling and footwork getting to the destination. Otherwise traveling by foot is required. Upon entering the The Shadow Fort enter the second hole in the ground leading to the Frontier Caverns. Travel through the Frontier Caverns to reach the Proving Grounds. A cutscene will occur showing the Hydra entering an underground arena accompanied by several goblins.