Route 12 is a long sea route on the east coast of Kanto. You can access it south of Lavender Town or east of Vermilion City, but it’s probably best to go south of Lavender to collect everything. When you enter the route house between Lavender Town and Route 12, go up stairs and talk with the kid to receive TM39 Swift. Swift is a normal-type attack that will never miss the target. Exit out of the route house to find several Pokemon Trainers.
South of the last Trainer is a sleeping Snorlax. The only way to wake up this Snorlax is with the PokeFlute. It will be awarded to you upon completing the Pokemon Tower quest. Speak with Mr. Fuji in his home to receive it.
Enter the house after the battle and speak with the fisherman inside. He will give you the Super Rod! This is the best fishing rod in the game, and will hook the rarest Pokemon. Continue along the dock to one more Trainer out in the open.