Celadon City lies to the west, past Saffron City. Once again, the road through Saffron City is blocked, but after fighting your way through a number of would-be Pokémon masters, you'll be able to use another underground path to bypass the guardhouse and reach the road beyond. Why is Saffron City locked up so tight? That's yet another mystery for another day.
The many roads to Saffron City are all blocked, so once you pass the challengers and catch yourself a Pokémon or two, take the tunnel connecting Routes #7 & #8. You never know what people may have misplaced in the dim lighting of the underground path. Your Item Finder will tell you if something's nearby, so take the time to explore a bit--there's an excellent chance you may find something valuable.
Next stop: Celadon City
What's up with Saffron?
Every road leading into Saffron City is blocked, and no one seems to know why. Are the guards posted at the gates to keep people in or out? What's being hidden? In any case, all the guards are quite thirsty. Perhaps there's something in Celadon City that could help in this situation.
The Underground path takes you to Route #7, which leads straight into Celadon City. This booming metropolis has everything a Pokémon collector might need, from a Department Store to a Game Corner for entertainment. If you've got the time to spare and want to build up your team, there's a wealth of Pokémon hiding in the tall grass just outside the city.
#58 Growlithe
#37 Vulpix
Fire Pokémon abound around here... Red gets a powerful Growlithe, Blue gets a swift Vulpix, and Yellow gets... nothing. Growlithe's a tough fighter with decent Fire attacks, who turns into one of Red's toughest brawlers when you power him up (into Arcanine) with a Fire Stone. But you may want to wait on that until he learns his best technique, Flamethrower, at Level 50.
The many-tailed firefox Vulpix, like Growlithe, evolves into its final form with the aid of a Fire Stone. Vulpixes may not be as tough as Growlithes, but they are a bit quicker, and they learn their best skill (Fire Spin, the Fire version of Wrap) as soon as level 42. Use the Stone then and you'll have a tough and versatile, good all around Ninetales.