Instructions
Go to Lavender Town and speak to the man in the radio station; he will inform you that he can't broadcast because the Power Plant isn't operating.
Head north on Route 10, go through the Rock Tunnel and head down the river that is outside the Rock Tunnel exit to reach the Power Plant.
Talk to the Power Plant manager; he'll tell you that a piece of machinery was stolen by a thief, who was last seen on his way to Cerulean City
Head back up the river to Route 9, which leads you to Cerulean City. Go to the Cerulean City Gym; the thief will run away from you here.
Head north from the city to Route 24, on the Golden Bridge. Defeat the thief here. He will tell you where the stolen piece of machinery is hidden: behind the life preservers in the Cerulean Gym.
Return to the gym, collect the stolen piece of machinery and head back to the Power Plant. Give the piece to the manager, go through the Rock Tunnel and speak to the manager there. He will reward you with the EX Radio Card, which lets you listen to the radio anywhere.
Go to Route 11 and play the Poke Flute from the radio in front of the sleeping Snorlax. He will wake up, allowing you to pass into Digglett's Cave.