The Bottom of the Sea is a level of the world map in Final Fantasy VII accessed from Part 2 onward, after the player obtains a Shinra Sub from the Huge Materia mission at the Underwater Reactor beneath Junon. The majority of the accessible areas are located near the center of the world, between the three main continents. Most of the locations in the Bottom of the Sea are optional; however, the player must enter it to obtain the Key to Ancients to use in the Forgotten City.
As soon as the player can access the underwater areas, the superboss Emerald Weapon is available to fight. Emerald Weapon is dangerous and will likely kill an unprepared party, especially when the party can first encounter it. Emerald Weapon often circulates the open area of the Bottom of the Sea near Junon, but it also can be found waiting in front of certain locations such as above the underwater crater or in front of the Gelnika; however, surfacing and re-submerging will cause it to move somewhere else. Emerald Weapon swims faster than the submarine, and therefore surfacing may be easier than trying to evade it if it is close.
There is a large underwater crater near the center of the world map. It is possible it was formed when Sapphire Weapon was defeated, or when Emerald Weapon landed underwater, much like the location where Ultimate Weapon is found near Junon created a massive crater.
The Junon Underwater Reactor can be seen underwater, but cannot be accessed via submarine.
If the enemy submarine was shot down in the minigame, visiting the sunken submarine southwest of Junon at the Bottom of the Sea will grant the player one of the four Huge Materia items.
The Gelnika is an optional underwater dungeon. The submarine must be directed west of Junon and through a gap to find it. Many of the game's rarer items can be found here, including the Highwind manual for Cid's final Limit Break, and the Conformer, Yuffie's ultimate weapon. It is also home to many of the game's toughest enemies whose morph items can be used for stat raising.
The Key to Ancients is located in the Bottom of the Sea in an underwater tunnel by the Icicle Area. If the player goes to the Forgotten City with Bugenhagen before retrieving the item, they will find the text "......(even sunlight can't reach)......(Key)" written in chalk beneath the Ancients' writing. Although it is part of a riddle, Bugenhagen gives hints and basically tells the player the Key to Ancients can be found underwater.
The player can access a location called ??? through the submarine. Traveling to the top of the eastern continent, and then beneath the continent, leads through a series of tunnels and emerges near a waterfall. The player can dock the submarine here and enter a cave behind the waterfall. Visiting the cave with Vincent in the party is needed to get the Chaos manual and the Death Penalty weapon. The cave can also be accessed with a number of varieties of chocobo, but not the Highwind.
- Emerald Weapon (boss)
While there are no random encounters underwater, Emerald Weapon appears here and is fought if collided with the submarine. The battle is under a time limit of twenty minutes to simulate the inability to breathe underwater. The Underwater Materia removes the time limit, obtained by trading a Guide Book item (morph from Ghost Ship) with the Kalm traveler.
The theme that plays in the Bottom of the Sea while traveling on the submarine is called "Secret of the Deep Sea" (深海に眠る秘密, Shinkai ni Nemuru Himitsu?).
Behind the scenes
Since the area visitable by the submarine is limited, there have been a number of rumors about how to access other areas of the underwater world map. One rumor is that the player would have to breed a silver chocobo, which could go underwater. One rumor surrounding this was that if the player traveled to North Crater while underwater, they could fight the boss Alpha-Leviathan. All such rumors are, however, unfounded.
If the underwater world map is accessed before the player gets the submarine, the player may appear as a number of other objects. One way to do this is through the Debug Room. One example is selecting an option to go to the Gelnika. Exiting the Gelnika will put the player on the underwater world map as the Key to Ancients. These objects can rise higher and travel over all terrain underwater (including over the sea walls), but cannot enter any locations or surface.
Since the underwater explorable area is smaller than the size of the overworld map, the underwater map area is repeated. The repeated areas are not normally traversable, however, if the player were to explore the top of the map they would be in an area that looks like the main portion of the underwater area. However, it is cut off at the top of the map.
Since the player cannot enter the menu when inside the submarine, the underwater area is never given a specific name as the overworld areas are. If oceans are removed from the world map via a cheat device, the player can run down into the canyons where the ocean would normally be, and accessing the menu from this position will reveal the area's name is "Bottom of the Sea". The text "Sea" also appears with the list of World Map names, so it is assumed that this would display if one could access the menu in the underwater World Map.