Instructions
Walk north from Viridian City into Route 2.
Walk into the entrance for Viridian Forest to the north.
Follow the path through the Viridian Forest area to reach the other side of Route 2. While in Viridian Forest you will have to walk through tall grass that will trigger wild Pokemon encounters and battle other Pokemon trainers. Prepare yourself for battle before entering the forest.
Exit Viridian Forest and walk north to the entrance to Pewter City.