Bottom of the Sea 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 . Locations . 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 " . Enemies . While there are no random encounters underwater , Emerald Weapon appears underwater and will be fought if collided with 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 . Musical themes . The theme that plays in the Bottom of the Sea while traveling on the submarine is called " Secret of the Deep Sea " .