In Mauville town, on the lower left middle portion, there is a house. Inside it was a scientist that will give you HM (Hidden Machine). It contains Rock Smash. Teach it to one of your Pokémon capable of learning. There is a road up on the Mauville town. On the far end there are two rocks. Use Rock Smash to go through the path. You can now continue your journey.
It is Altering Cave which you can enter only after you beat the Pokemon league.
beat the Pokemon league
Beat the elite four the cave should open.
when your in the cave where you get ditto (in fossil manics house) go in the cave after you beat the elite 4 then go all the way right
please help i need to beat pkmn emerald
after you beat the Pokemon league go where the shoal cave is then look to your left and the is a dive spot dive and go through and then go up then there is a cave and that is the marine cave.
There is no Pokemon in the Cave of Origin in Pokemon Emerald.
how 2 get in the under warter cave on Pokemon emerald
this is either in fire red or emerald but it brings you to the next reidion after you beat the elite four!
dragon poisonyou get it in cave of origin but u have to beat the 8th gym to use it.
you beat a cave and use dive in mossdeep city thats all!
it is a cave