The Undersea Ruins are located beneath Undella Bay and has four possible entrances. Once inside the ruins, you will find that you have a limited time to navigate the various areas. Throughout the area are a number of columns which detail various legend in a special form of cuniform. These can be translated in Pokémon Black 2 & White 2 using a gift from Plasma Sage Zinzolin

Special Moves used in Abyssal Ruins:
Surf
Strength
Dive
Flash