Now that you have access to Submarine, you can explore the ocean floors. However, many ocean floor areas are enclosed, so you'll have to dive from the surface.
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There is an old man living in this cave who can tell you a summary of your journey.
Visiting this place is required for the Adventurous Wayfarer achievement.
Tower of Walse
This dungeon is optional, and you can visit anytime you want to challenge the boss the hard way.
Trivia: there is an optional scene if you visit Carwen and interact with a girl standing at the stairs in front of the pub. She'll ask you if she is pretty. Answering "Yes" will make her push you away and transform into Bartz or whoever your avatar is.
Tower of Walse is in the same location but on the ocean floor. You'll have to dive from the surface near Carwen to access this area.
- Once you enter, you have 7 minutes to clear the dungeon. So don't worry about bestiary because you've already fought most of them. Equip Masamune + Scram to easily flee the battles.
- On 4F, climb the column to 5F and open the chest to reset the timer.
- When you interact with the crystal shard, answer "No" to start the battle.
Boss: Famed Mimic Gogo
Steal: Gold Hairpin (rare)
Note: Gold Hairpin is a rare item; however, you've already got two, so I think it's not worth it to steal another one from him.
There are 2 ways to approach this boss.
The easiest way is to do NOTHING. His specialty is mimicking, so when you do nothing, he has nothing to mimic. After a few minutes, he'll get bored and give up.
The hard way is to properly fight him. However, he'll act like a superboss. The strategy involves using Spellblade + Silence; this will prevent him from casting any magic back at you.
Halfway through, he'll start acting on his own by casting powerful spells.
Use Teleport to leave the castle.