【How-to】How to get to cinnabar island

Explore Route 21. Go to Pallet Town and get into the water, then surf southward to reach Route 21. In the grass to the right, you can catch Pidgeotto, Rattata, Raticate, Bellsprout, Weepinbell, Tangela, and others. Surf southward, and there is a small island to the southeast where you can get a Hyper Potion.