Pokémon Red and Blue/Diglett's Cave

With Route 11 blocked, you must take the roundabout route to Lavender Town. Diglett's Cave connects Route 11 with Route 2, emerging near Viridian Forest. Head north to Pewter City, then east to Cerulean City and Route 9. Now that you know how to Cut, be sure to visit the secret lab behind the Pewter City Museum.

Diglett's Cave encounters
Diglett	95%	95%	95%
Dugtrio	5%	5%	5%

Through the cave

#50 Diglett
You don't really see a lot of Ground-type Pokémon, but that's largely due to a shortage of Ground skills. Diglett and Dugtrio don't really have anything you haven't already seen: Dig (at level 19) is great, but that's all that's interesting for a long time. Certainly worth picking one up though.

Diglett's Cave connects the west side of Route #11 and the north end of Route #2, near Viridian Forest. The path is easy, but Diglett and Dugtrio can be annoying, so remember: Flying creatures are immune to Ground-based attacks, even Dig.

Having Digletts leveled between 15 and 22 and Dugtrio between 29 and 31 this is a truely awesome time to level up Pokémon, especially Flying. Pokémon in the Pidgey, Spearow, Zubat families can level up fast as well as Farfetch'd, Gyarados, and Butterfree. Beedrill unlike the others, is not classed as a flying Pokémon. They are still classed as Bug and Poisen, so they are still vulnerable to Ground attacks.

Back to Route #2

File:Pokemon RBY Route02.png

Route #2

When you exit Diglett's cave, you'll be in a familiar place, the north end of Route #2 near the exit of Viridian Forest. Now that you have Cut, the remainder of Route #2 is available to you.

The building south of the cave exit has a guy who is willing to trade you a rare Mr. Mime, in exchange for an Abra in Red/Blue, or a Clefairy in Yellow.

Further south, there's another building in which you can get HM 05, which contains Flash, the item you came for. This is used primarily to light caves, but in battle it will lower the Accuracy of your opponents' attacks. Its current owner, another one of Professor Oak's aides will only fork it over if you have 10 or more Pokémon. Below that house are two item balls which contain an HP Up, and a rare Moon Stone.

While you're in the area, head back to Viridian City and cut down the tree in the lower left corner. Walk inside the area and talk to the man, and he'll give you TM 42 with that Dream Eater for your Drowzee. Cut aside another tree in Pewter City to get the Old Amber from the Museum Curator. When that's all done, either travel through Mt. Moon, or cut back through Diglett's Cave, and head to Cerulean City.

#122 Mr. Mime
Since it's an easy trade, you should definitely try to pick up a Mr. Mime. He doesn't have many good skills and can't evolve, but his trademark Psychic attack, Substitute, where he creates a clone that fights for him, is pretty cool.