Pokémon FireRed and LeafGreen/Route 8

Route 8 usually leads directly to Saffron City, but once again, the direct passage ahead of you is blocked, forcing you to find an alternate way. No problem. Just go into the small cottage in the northwest and you will discover an underground passage that leads to Route 7, which in turn connects to Celadon City. But before you can get there, you need to fight a bunch of trainers that block your way.