Rock Tunnel is the only avenue between Route #10 and Lavender Town. Unlike the caverns beneath Mt. Moon, Rock Tunnel is pitch black, and you must rely on the Flash technique (HM 05) to light your way. Use the labeled maps to follow the ladders through the tunnel to the exit. The tunnel has two levels, but there really is only one main path.
The wild Pokémon in Rock Tunnel seem to attack more often than their above-ground cousins, and if you're being attacked every few steps, it may take you awhile to reach medical attention. For that reason, it's a good idea to bring either a Pokémon that knows Dig, or plenty of Escape Ropes just in case you need to make a quick getaway. If you don't have either of those, this would be a good time to try the Repel potion, which keeps minor Pokémon at bay.
You'll have a much tougher time, however, avoiding the many trainers lurking in the shadows. You'll have to use Flash if you want to see where you're going in here. It's possible to proceed without it, but you'll probably want the light so you can avoid some of this area's tedious, difficult trainer encounters. If you want to avoid a duel, walk a path that's far away from the trainer or that's out of the trainer's line of sight.
They're not a common sight in any version, but anyone can track down and capture a Machop with a bit of effort. Machops are strong on offense and HP and only get stronger as they evolve: Into Machoke at level 26, and then into Machamp once they're traded.
Onix is a fair Rock-type Pokémon to have. They have exceptional Defense and decent Speed, but rather poor HP, Offense, and Special Defense, making it rather susceptible to Water attacks. It learns Rage at level 25 which can be a useful Normal-type move when you have no other options.
Machop
Geodude
