It can be found in the Solaceon Ruins.
you have to go to the socaleon ruins or whatever
iron island
first get out a there go to hertarome then veilstone
You find it in the solaceon ruins after you catch all the unown.
You get it from Riley on Iron Island.find it the solecean ruins
The Solaceon Ruins.
no regigigas was a new Pokemon in Pokemon platinum
Arceus
I think you have to find a special pokemon
Iron Mountain isn't in Pokemon Platinum
Regirock can be found in the Rock Peak Ruins (on Route 228) Registeel can be found in the Ironhead Ruins (Iron Island) Regice can be found in the Iceberg Ruins in Mt Coronet.
lol there are no eterna ruins that was just in the anime.
The only way to get the 3 Regis in Pokemon Platinum Version is if you have the Regigigas given away at Toys 'R' Us. Only that exact Regigigas will activate the other 3.\actually Registeel is in the Iron Ruins inside of Iron Island B3F.
in the solaceon ruins.
you get it at the solaceon ruins at the end of it
you go in from the veilstone way