Walkthrough
You won't be able to advance further within the Pokemon Tower in Lavender Town without defeating Team Rocket in the Rocket Hideout below the Celadon City Game Corner. In order to gain entrance to the Rocket Hideout, simply defeat the Team Rocket Grunt in the back of the Game Corner. After you do, you will be able to remove the poster in the Game Corner to find the entrance to the hideout.
The Rocket Hideout is one giant maze full of Team Rocket Grunts looking to prevent you from reaching their Boss on the bottom level. In order to reach the Team Rocket Boss, you will need to use the elevator lift. In order to use it, however, you will need to find the Lift Key. It will be held by one of the Team Rocket Members found within the hideout, practically forcing you to defeat every last one of them on your way to the Boss. Defeat Boss Giovanni to obtain the Silph Scope that can be used to completely ascend the Pokemon Tower.
Pokemon Trainers
Entrance:
Team Rocket Grunt: Level 20 Raticate, Level 20 Zubat
Basement Floor 1:
Team Rocket Grunt: Level 21 Raticate, Level 21 Raticate
Team Rocket Grunt: Level 21 Drowzee, Level 21 Machop
Team Rocket Grunt: Level 19 Rattata, Level 19 Rattata, Level 19 Raticate, Level 19 Raticate
Team Rocket Grunt: Level 20 Grimer, Level 20 Koffing, Level 20 Koffing
Team Rocket Grunt: Level 22 Grimer, Level 22 Koffing
Basement Floor 2:
Team Rocket Grunt: Level 17 Zubat, Level 17 Koffing, Level 17 Grimer, Level 17 Zubat, Level 17 Raticate
Basement Floor 3:
Team Rocket Grunt: Level 21 Machop, Level 21 Machop
Team Rocket Grunt: Level 20 Rattata, Level 20 Raticate, Level 20 Drowzee
Basement Floor 4:
Team Rocket Grunt: Level 21 Koffing, Level 21 Zubat
Team Rocket Grunt: Level 23 Sandshrew, Level 23 Ekans, Level 23 Sandslash
Team Rocket Grunt: Level 23 Ekans, Level 23 Sandshrew, Level 23 Arbok
Boss Giovanni: Level 25 Onix, Level 24 Rhyhorn, Level 29 Kangaskhan
Items
Basement Floor 1:
Escape Rope: On Ground
Hyper Potion: On Ground
PP Up: ItemFinder
Basement Floor 2:
X Speed: On Ground
Moon Stone: On Ground
TM12: On Ground
Super Potion: On Ground
Basement Floor 3:
Rare Candy: On Ground
Black Glasses: On Ground
TM21: On Ground
Nugget: ItemFinder
Basement Floor 4:
TM49 On Ground
Max Ether: On Ground
Calcium: On Ground
Lift Key: On Ground
Net Ball: ItemFinder
Nest Ball: ItemFinder
Silph Scope: Defeat Boss Giovanni