Go to the Galactic Veilstone Building in Veilstone (of course in Veilstone) and beat Cyrus there. Then the painting should be busted open. I was stuck there too. I looked everywhere and couldn't find it
beat Cyrus the intergalactic hussy
You need to of released the lakePokemon (Azelf, Mesphrit, and Uxie). The you can go there and the cave painting will be demolished.
The leader of team galactic should break through it and the looker will talk to you and then you go through the entrance and you go outside and battle Cyrus with your rival and then dialga palkia and giratina appear and you go into the distortion world.
To get to the top of Mt. Cornet you have to beat the team Galactic Eterna City and Veilstone buildings(otherwise there will be a cave painting blocking the path in Mt. Cornet) and enter Mt. Cornet from the Oreburg-Hearthrome City entrance(This is the ONLY entrance to the summit of Mt. Cornet. The other entrance takes you on the path to Snowpoint City). You need the HMs Rock Climb, Rock Smash, Strength, and Surf (Defog won't work in the cave). Also, when you get to the crumbled cave painting, Looker will give you a Black Flute, which lowers the chance of you running into wild pokemon.
The turn back cave in Pokemon Platinum is in Seodoff Spring near veilstone city
go to mt. cornet and go a cave
beat Cyrus the intergalactic hussy
Go to the Galactic Veilstone Building, defeat Cyrus, and then the painting should be busted open.
You buy a gameshark ad cheat through it.
find palkia come back
You need to of released the lakePokemon (Azelf, Mesphrit, and Uxie). The you can go there and the cave painting will be demolished.
The leader of team galactic should break through it and the looker will talk to you and then you go through the entrance and you go outside and battle Cyrus with your rival and then dialga palkia and giratina appear and you go into the distortion world.
Mount Cornet on Hearthome city side
To get to the top of Mt. Cornet you have to beat the team Galactic Eterna City and Veilstone buildings(otherwise there will be a cave painting blocking the path in Mt. Cornet) and enter Mt. Cornet from the Oreburg-Hearthrome City entrance(This is the ONLY entrance to the summit of Mt. Cornet. The other entrance takes you on the path to Snowpoint City). You need the HMs Rock Climb, Rock Smash, Strength, and Surf (Defog won't work in the cave). Also, when you get to the crumbled cave painting, Looker will give you a Black Flute, which lowers the chance of you running into wild pokemon.
there is no cave of time
The turn back cave in Pokemon Platinum is in Seodoff Spring near veilstone city
Hippopotas is located in the Ruin Maniac cave in Pokemon Platinum.