You go nere it and use the hm dive and find a cave enterents go in it then go to ur Pokemon that's knows the hm dive hit use dive. Then u will go up then surf to the other end of the cave and the you are there
You can find Steven near the gym is Sootoplis City. When you find him, he will take you to the cave of origin.
you cant
In the cave of origin which is in sootoplis city.
at either mossdeep city,sootoplis or ever grande city.
in the cave in sootoplis city when your going to fight groundon
you can get it [rarely] while using dive in the grass around sootoplis city or fishing around the big city
Don't you mean "How to get to Sootoplis City in Pokemon Ruby?" Oh it's simple, get dive and dive underwater near Mosdeep City and find the path, then keep going down until you find a cave, go in the underwater cave and then dive again and there you are!
You need waterfall, which can be obtained in sootoplis's cave origin. Or get a goldeen or seaking.
Go to sootoplis city to battle Gorudon and beat the last gym leader.
in sootoplis
You catch him in the Cave of Origin in Sootoplis
in a cave at the town after sootoplis