Pokémon Red and Blue/Route 4

'After the ordeal in Mt. Moon, Route #4 will probably seem like a walk in the park. There are no trainers to challenge you and only one area where you can run into wild Pokémon. Be sure to collect Whirlwind (TM 04) before you jump the hedge to reach Cerulean City. After you jump it, you won't be able to jump back over it to backtrack along Route #4'

Next stop: Cerulean City
There's nothing particularly interesting in Route #4. All you'll find at this point is a Poké Ball with TM 04 in it, which teaches a Pokémon the battle ending (but relatively pointless) Whirlwind skill.

Be careful: When you jump down the wall in the Southeast (and you'll have to in order to progress), you won't be able to go back!