Otomai's Ark

 is a dungeon filled with pyrates.

Access
The dungeon is found at (-55, -4) or somewhere around, in the eastern part of Bottomless Peat Bog. There's an ancient shipwreck you are to enter and follow thru to the very end, where NPC is guarding the entrance. Entering requires a Otomai's Arch Key, which is consumed.

Dungeon levels
The last room contains a mob leaded by Gourlo the Terrible which has 200% resists to all atacks, as well as 2200 HP, 10 AP, 6 MP and a bunch of deadly spells at hand.

Benefits
Painful death.