I think you need certain pokemon and dive to get to it. when you get to the cave, you must walk a certain pattern
In Diamond you can't catch Regirock, you have to migrate it from Pokemon Ruby, Sapphire, or Emerald.
Regirock, and finally Registeel.
u have to migrate them from ruby Sapphire emerald
You can't catch a sentret in Ruby version, but you can catch one in Emerald version.
you import it from em/ruby/saph and catch it in pal park
I don't think you can get regirock in pokemon ruby.
You can only get a regice, regirock, and a registeel by migrating them from ruby or Sapphire. If you migrtate these Pokemon you can also catch regigigas.
You can catch Groudon,Rayquaza,Latios,Deoxys,Celebi,Jirachi,regiice,regirock,registeel,and Mew
to get regirock in Pokemon platinum, you have to upload it from ruby, Sapphire, or emerald.
You can't.You have to trade it from Pokemon Ruby Version
The legendaries you can catch in Pokemon Ruby without trading or going to an event are Groundon, Rayquaza, Latios, Regice, Regirock, and Registeel.
in ruby there's groudon, raquaza, regirock, (if you consider it a lengendary) regice, and regirock