There is no secret chamber on Cinnabar Island. Although there is an obvious hole at the top, it does not lead to a secret chamber. The hole cannot even be accessed, but only walked around.
well I've plated quite a while and i have never found a hidden tomb unless your referring
to the seafoam islands
in the kanto region ,on the island of cinnabar
you have to meet gym leader from kanto in Cinnabar island
Professor Oak gives you it after you get 16 badges
On cinnabar island it can be turned into a Pokemon
you can't find Cinnibar Island in Platinum, its in the Kanto region, if you want to play the games, the recent ones are FR and LG (Pokemon Fire Red and Pokemon Leaf Green) on GBA, but next year sometime if your in Europe (it may be earliar if your in the US) Pokemon Dawn Gold and Soul Silver are coming out on DS and DSi which are remakes of Gold, Silver and Crystal
The Cinnabar Island
You can find it on Cinnabar Island.
go south of pallet town
You can find one on Cinnabar Island.
in the kanto region ,on the island of cinnabar
Blaine. Seafoam Island (Cinnabar)
surf at the south of pallet town
From Pallet town surf South and it should be there.
You can find it at cinnabar island but you have to have the move rock climb to get it
building near Pokemon center on cinnabar island
surf through passage ways in front of the island
cinnabar island need 7 kanto badges