Final Fantasy V/The Water Crystal
Once you have Hiryuu, fly to the south to the town of Worus. Enter the castle and speak with the king. When you do so, a meteor will land near the tower to the north.
Enter the town of Worus and purchase and supplies needed before heading to the tower. There are several new spells (most of which can't yet be cast), as well as better armor and weapons.
 The tower
When the king heads to the tower, it will be open for you; however, the meteor is still closed for now. Fly to the tower and enter.
The tower doesn't contain wondering monsters, but there are a few secrets. On the fourth floor, you can enter the water on the left and climb the vines to get a Silk Robe.
The fifth floor has a savepoint, before you encounter any monsters.
The eighth floor appears to be a dead-end, but had three climbable vines. The center is a dead-end path, The left leads to a silver ring, and the right leads to the next floor and an Ether.
 The water crystal
Once you pass the ninth floor and enter the crystal room you will see Galura approach the crystal.
Galura has 1200 HP, and mainly uses physical attacks. From time to time, he will use the Rush attack to inflict extra damage and HP down status.
The crystal will shatter after Galura is defeated. You will be able to collect new jobs from the shards: Berserker, Mystic Knight, Red Mage, Summoner, and Time Mage. The Tower will begin to sink as soon as you collect the last reachable shard.
You will now be able to use the meteor to reach Karnak.
 Worus Castle Items
There are a few items to collect within Worus castle, however, it is guarded by a dangerous monster. As such, you should save your game before entering, especially if you have low-level characters.
From the main castle forum before the throne room, head to the right and take the stairs down. Take the north-east exit and head down the stairs. Go down the path; you can head to the right to collect 2000 Gil and the Drag spell, and down the left path to get an Elf cape.