Crystalis/Shyron

From Swan, cross the Goa plains to the west until you arrive at Mt. Hydra. Once there, keep going west until you find a narrow lava flow. Despite the heat, the Sword of Water can still freeze an ice bridge here. Pass through the short cave passage. Once you emerge, use Change to assume the form of Stom. This way, the guards will let you pass into Shyron.

Shyron
You will find plenty of familiar people here, including Akahana, who reveals he is a Draygonian from Goa who left because he didn't like the regime. The stores here stock some very rare stuff at surprisingly low prices (the Magic Ring at $800 and the Sacred Shield at $6000, $3000 less than at Amazones). If you have the cash, splurge because the bargain isn't going to last...

At the north end of the village is the Temple. Here, you will meet Zebu who tells you to delve in the heart of the volcano, a region known simply as Styx. He gives you the Key to Styx so you can enter in search of the Sword of Thunder. Leave Shyron and start searching for Styx.

Styx
Make your way back to the initial area of Mt. Hydra. Now take the north fork into the cave network. Fortunately, the way to Styx isn't that difficult. Just take the left branch and exit, then follow the outer path all the way around (creating an ice bridge along the way) and taking the left at the fork until you reach the gate to Styx. Use the key to unlock the gate then delve inside.

The first thing you should see are lines of statues all shooting rocks at insane speeds. The only way you'll be able to get through this gauntlet is to employ the Barrier spell. It's rather expensive, but it's the only way through. Conserver magic by using it in bursts: just long enough to clear each barrier.

You're not equipped to get the item in the right fork, so go left instead. Use Barrier again to protect yourself against the Sorcerer's spells while you quickly hack him to pieces. The path in the next area is pretty straightforward. Follow the riverbank until you can find spots to cross using ice bridges. Eventually, you'll arrive on the right side of the river where you can find a way upstairs.

Be careful here. The Giant Eyes cast Petrify spells while the Killer Moths, like before, scatter paralyzing dust when they die, and they're everywhere. The right path leads to lots of painful spikes, so instead go up and wait for the moving platform to cross the gap; otherwise, you'll fall back to the river area. Make it across the gap, and you only need to make your way past a short stretch of the spikes; the Rabbit Boots can help minimize the damage. But don't open the chest yet if you're not quite at level 12. Once you take the Sword of Thunder, the Elders will teleport you back to the Temple at Shyron.

There, you will meet Azteca, the leader of the Elders and founder of the rebel movement. He and three of the Elders will fill in some of the blanks on the time between your stasis and now: about how Draygon recruited the Four Finest and how he plans to exploit Mesia's power. Your next step is to take the fight to Draygonia. Proceed to Draygonia's capital: Goa.