Walkthrough
Rock Tunnel is located in the middle of Route 10, and you'll have no choice but to venture through it since it's the only way to reach Lavender Town at this point in the game. Since the cave is pitch black, you will need to use the Light Up Technique to be able to see at all. Tons of Wild Pokemon and Trainers can be found within Rock Tunnel.
Wild Pokemon
Standard Walking:
Zubat (20%): Levels 18-23
Geodude (20%): Levels 18-23
Golbat (10%): Levels 18-23
Machop (10%): Levels 18-23
Graveler (10%): Levels 18-23
Onix (10%): Levels 18-23
Rhyhorn (10%): Levels 18-23
Cubone (9%): Levels 18-23
Kangaskhan (1%): Levels 18-23
Standard Walking - Special Spawns:
Charmander: Levels 18-23
Trainers
First Floor:
Poke Maniac Ashton: Level 23 Slowpoke
Camper Lenny: Level 22 Growlithe
Hiker Oliver: Level 23 Onix, Level 23 Sandslash
Hiker Claus: Level 23 Machop, Level 23 Rhyhorn
Picnicker Leah: Level 22 Nidorina
Camper Leroy: Level 22 Nidorino
Picnicker Dana: Level 22 Meowth, Level 22 Vulpix
Basement Floor 1:
Poke Maniac Winston: Level 23 Kangaskhan
Black Belt Dudley: Level 24 Onix
Black Belt Eric: Level 24 Mankey, Level 24 Poliwhirl
Hiker Allen: Level 23 Geodude, Level 23 Graveler, Level 23 Onix
Poke Maniac Cooper: Level 23 Ivysaur
Ace Trainer Sofia: Level 24 Vulpix, Level 25 Kadabra
Black Belt Steve: Level 24 Machop, Level 24 Machop
Ace Trainer Charlie: Level 24 Diglett, Level 25 Flareon
Obtainable Items
First Floor:
Poke Balls: Defeat Poke Maniac Ashton
Repel: Near Poke Maniac Ashton
Great Balls: Defeat Camper Lenny
Poke Balls: Defeat Hiker Oliver
Escape Rope: Near Hiker Claus
Poke Balls: Defeat Hiker Claus
Great Balls: Defeat Picnicker Leah
Great Balls: Defeat Camper Leroy
Stardust: Near Picknicker Leah & Camper Leroy
Great Balls: Defeat Picnicker Dana
Pearl: Near Picnicker Dana
Basement Floor 1:
Poke Balls: Defeat Poke Maniac Winston
Revive: Far Southwest Corner
Dire Hit: Near Black Belt Dudley
Poke Balls: Defeat Black Belt Dudley
Great Balls: Far North West Corner
Poke Balls: Defeat Black Belt Eric
Poke Balls: Defeat Hiker Allen
Poke Balls: Defeat Poke Maniac Cooper
Full Heal: Near Poke Maniac Cooper
Ultra Balls: Defeat Ace Trainer Sofia
Poke Balls: Defeat Black Belt Steve
Super Potion: Near Black Belt Steve
Ultra Balls: Defeat Ace Trainer Charlie
Stardust: Near Ace Trainer Charlie
Post Game
Walkthrough
After defeating the Elite Four and starting the Master Trainers Challenge, you will find a couple of Master Trainers within Rock Tunnel. In total, there will be two Master Trainers to defeat.
Trainers
First Floor:
Hiker Irwin (Master Trainer): Level 65 Geodude
Basement Floor 1:
Scientist West (Master Trainer): Level 70 Zubat