How do you get into the cave of origin that old man is in the way. PL..

Go to mossdeep city and go down until you see water where you can dive. Dive down and follow until you see a opening to a underwater mountain go in there. You will se the submarine that the team magma stole from cap. Stern. Dive up and go into the underwater cavern(u will need strength, rock smash, surf, and I think flash).

Follow that until you get to a part where you see fog follow that down until you come face t face with Groudon. When you're done battling team magma leader Maxie you will need to go to Sootopolis city. Go to the left of the gym and you will see steven and the gym leader speaking to each other they will have you follow them to the Cave of Origin. You can go into it and then you have to follow until you get to a room with Groudon that is where you have a chance to catch it. Then you can battle the Gym leader which uses ice and water pokemon. Here is the way you have to go to get there.
1st floor.
__F__
|6 7 *|
|5 4 3|
|* 1 2|
--S--
2nd floor.
______F______
|6 7 8 K J I H|
|5 * 9 A B C G|
|4 3 2 1 * E F|
------S------
3rd floor.
__________F__________
|V W Z 1 4 5 H G D C B|
|U X Y 2 3 * I F E * A|
|T S P O L K J 4 5 6 9|
|* R Q N M 1 2 3 * 7 8|
----------S----------
Hope I helped.

You get into the cave of origin after you beat the Team Magma leader in the underwater cavern then you go to sootopolis and talk to steven and he will take you there.

First of all you got to go to lylcove and surf downwards...Then you use dive so your under water then keep going down then there is a cave so go in there and then you see a sumbermarine press B so then you get out of the water then go straight and then your in a cave then after get past them all (team magma) you see Groundon but he flys away and then automaticually you go in water so then fly 2 Superpolis and then you can go in the cave

You have to find the underwater cavern and battle the team Magma leader. Then Groudon will awaken and you will be taken outside. Go to the cave of origin and you will be able to go inside. Groudon is inside, so either catch him or kill him!
Hope I helped!

You go to the submarine which team aqua steal and yo press b and you fight the boss of team aqua



Hope I helped :D

Do what other guys said, also how to you do this on omega ruby?

So I did not understand what you guys were saying so what I did was I swam around until I hit route 127 but I kept on swimming until I hit route 128 and the sea floor cavern is left to Ever Grande City. I hope this helped!