Sea City

Sea City is a city located in the eastern region of the New World.

The Lizard Man Heroes Arc
Among the countries and cities listed in the New World's incomplete map by Ainz Ooal Gown, Sea City happens to be one of them alongside Eryuentiu.

The Invaders of the Large Tomb Arc
Sea City is mentioned by Platinum Dragon Lord during his discussion with Rigrit Bers Caurau concerning who or which person he should ask for help. He stated that the high chance of waking some unknown female individual up from her slumber in Sea City is a better choice to do than requesting aid from his fellow Dragon Lords.

Layout
Platinum Dragon Lord stated to Rigrit that what lies in the deepest level of the Sea City is apparently an unknown female individual sleeping. This may hint on the possibility regarding a layer of levels within the Sea City for one must transverse through in order to reach the deepest part of it all.

Trivia

 * Based on Platinum Dragon Lord's response to Rigrit, it seems possible that the person he was hoping to seek aid from against Players is most likely located in Sea City.