The Abyssal Ruins are locations found in the video games "Pokémon Black" and "Pokémon White." They are found underwater in certain areas and require a Pokémon with the "Dive" ability to access.
There are four separate Abyssal Ruins, but all are located in Undella Bay. They can be found by diving when over dark patches of water.
The Abyssal Ruins have some unusual rules of movement. Players are only allowed to travel 500 steps in total before they are automatically washed out by a tidal wave. The game will provide the player with a reminder message about a dull echo approaching every 100 steps. Players can return immediately to the same ruin once washed out but will have to start from the entrance again. Each ruin also has four levels in total, but players can only descend a level if they walk directly to the center of each floor without exploring off to the sides or backtracking. The "Flash" and "Strength" abilities will be needed to get through the later floors.
The main appeal of exploring the ruins is that they contain some rare and valuable treasures. Plates found within the ruins raise the attack power of the attack type they are named after by 20%. Relic items found within can also be sold for a large amount of money.