The Bottom of the Sea is a level of the world map in Final Fantasy VII. The area can only be accessed from Disc 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 of the Bottom of the Sea are located near the center of the world, between the three main continents. Most of the locations in the Bottom of the Sea are entirely 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 will be available to fight. Emerald Weapon is dangerous and will likely kill an unprepared party, especially when the party may 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 moves faster than the submarine and therefore surfacing may be easier than trying to move out the way if it is close.
There is a large underwater crater found 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 dungeon underwater. It appears underwater without the player having to watch the FMV at the Airport in Junon, and the player can still watch the FMV showing the Gelnika's take-off even after the player has visited it, indicating these are two different planes of the same model (the one which can be seen leaving Junon is likely only carrying the last Huge Materia to Rocket Town). To find the Gelnika, the submarine must be directed west of Junon and through a gap. 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.
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 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. If the player travels to the top of the eastern continent, and then travels beneath the continent they can go through a series of tunnels and emerge near a waterfall. The player can dock the submarine here and enter a cave behind the waterfall. This cave is vital in order to get the Chaos manual and the Death Penalty weapon, Vincent's final Limit Break and ultimate weapon, respectively. The cave can also be accessed with a number of varieties of chocobo, but not the Highwind.
While there are no random encounters underwater, Emerald Weapon appears underwater and will be fought if collided with in the submarine. The player fights Emerald Weapon underwater with a time limit of twenty minutes to simulate the inability to breathe underwater. The player can receive an Underwater Materia, which will remove the time limit, by trading a Guide Book item 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?).
- Since the area visitable by the submarine underwater is limited, there have been a number of rumors about how to access other areas of the world map underwater. 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 traversible, 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. However, 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. Accessing the menu from this position will reveal the area's name is "Bottom of the Sea".