From Bulbapedia, the community-driven Pokémon encyclopedia.

Slowpoke Well (Japanese: ヤドンのいど Yadon Well) is a cave located at the edge Azalea Town. It is said that a Slowpoke from the well ended a drought that plagued Azalea 400 years before the games' events by Yawning. Slowpoke Well is where the player first encounters the revived Team Rocket, who are cutting off the tails of Slowpoke to sell at their HQ in Mahogany Town.

After Kurt is injured while trying to stop Team Rocket, the player has to defeat the Grunts and rescue the kidnapped Slowpoke. Later in the game, after the player as acquired both Surf and Strength, they can explore the lower floor of the well. There is a man on an island who will give players a King's Rock if they talk to him.

Johto
Gym:	Violet City | Azalea Town | Goldenrod City | Ecruteak City | Cianwood City | Olivine City | Mahogany Town | Blackthorn City
Other:	New Bark Town | Cherrygrove City
League:	Indigo Plateau* (games) | Mt. Silver (anime)
Routes:	28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46
Landmarks:	Dark Cave | Sprout Tower | Ruins of Alph | Union Cave | Slowpoke Well | Ilex Forest | Radio Tower | National Park
	Tin and Brass Towers | Sparkling Lighthouse | Battle Tower | Whirl Islands | Mt. Mortar | Lake of Rage | Ice Path | Dragon's Den