- Main article: Kanto Route 22
Route 22 is the path that leads to the badge checkpoints for the Pokémon League. Of course, you're unable to do that yet so the most you can do for now is catch some Pokémon and fight your rival. The encounters here are Rattata, both Nidoran genders, and a low chance of Spearow.
Second Rival Battle
The rival battle is totally optional but if you have two Pokémon with level 9, it shouldn't be any problem. You can bring Potions too just to make sure you win. In this rival battle, a Charmander start would be at the most disadvantage as Squirtle learns Bubble at exactly Level 8. Squirtle is the most ideal start as you can pick up Spearow prior to the fight and it immediately learns Peck in early levels to counter the rival's Bulbasaur. Gust is considered a Normal-type move in Generation 1 so Bulbasaur starts shouldn't have too much of an disadvantage. One thing to watch out is the rival Pidgey's Sand Attack, save before the fight just in case you get extremely unlucky with trying to hit your moves. As soon as you finish, head back to Viridian City, heal up, and head North to Route 2.
- Main article: Kanto Route 2
For now, Route 2 is a straight road to Viridian Forest. The eastern path is currently not accessible until you get HM Cut or enter through Diglett's Cave. There's not really much noteworthy things in the route aside from new encounters, being Weedle in Red and Caterpie in Blue. It's probably not worth looking for them here as they have a better encounter rate in the forest.
- Main article: Viridian Forest
Viridian Forest is slightly complicated with certain paths leading to dead ends, but it shouldn't be too hard to traverse as long as you don't go around in circles. This is also the first location where you will have trainers approach you for battles. They will approach you if you go within their line of sight (which also means some fights are avoidable) and they can also carry up to a maximum of 6 Pokémon just like you. If you brought a Spearow, the forest shouldn't be much of an issue for you and if you started with Bulbasaur, this is the ideal time to level it to 13 so it can learn Vine Whip for the next gym. It is also recommended that you stock up on 2-3 Antidotes prior to entering Viridian Forest unless you're fine with taking multiple trips to the Pokémon Center every time you get poisoned. Consider picking up a Caterpie (NOT Metapod) as it's a rather solid early-game Pokémon, it evolves to a Butterfree at Level 10 and learns Confusion at Level 12
As mentioned earlier, Caterpie/Weedle/Metapod/Kakuna are more readily available in the forest in both versions (Caterpie/Metapod rarer in Red and Weedle/Kakuna rarer in Blue). Pikachu is also a new encounter, which is a decent choice for Bulbasaur starts to counter Flying-types.
The items around the forest aren't very special. Most can be already bought in the Pokémart but I'll still list them out just in case you want to clear it. The correct route to exit the forest is to the east of the entrance, but if you head north-west you can pick up an Antidote. Head back to the entrance and go east then north to fight your first couple trainer battles. If you levelled up your Pokémon to Level 9 as instructed prior to the rival fight then there shouldn't be too much issues aside from getting poisoned. After your second trainer battle, continue heading north to the non-grassy area to pick up another Antidote. Don't bother going around the non-grassy area to the east and just head straight west then south as it just leads to the same area. It's now mostly a linear path until you reach an area with a sign, head south-east to pick up a Potion then continue heading north-west to your final trainer battle and exiting the area.
There are two main buildings in Pewter City, namely the Pewter Gym and the Science Museum. The Science Museum can be entered by paying 50 but there aren't actually anything you can do inside. Once you receive HM Cut when you reach Vermillion City, you can retrieve the Old Amber inside and revive it to an Aerodactyl at a lab in Cinnabar Island.
First Gym Badge
- Main article: Pewter Gym
There is only one trainer to battle prior to the gym leader Brock. The fight should be rather simple for Bulbasaur/Squirtle starts, as Bulbasaur learns Vine Whip at Level 13 and Squirtle learns Bubble at Level 8. However the situation is different for Charmander. Fortunately, unlike Generation 3 Brock's Pokémon doesn't learn any Rock-type moves that can be a massive threat to a Charmander. A Level 11 Charmander can actually solo the Gym with enough Potions. The strategy is to keep using Growl against Geodude and heal up with Potions until Geodude reaches the lowest attack possible and then keep using Ember. For Onix, use Ember constantly and switch to Growl when it uses Bide.
After the gym, heal up and exit to the east of Pewter City to enter Route 3.