Pokémon Red & Blue walkthrough

12 parts, one per checkpoint Pokémon Red & Blue’s own documentation defines: the areas each one opens, the wild Pokémon and trainers in them, and the fight at the end of it. Everything here is read off the game’s own files, so anything it doesn’t state isn’t claimed.

1. Part 1: Just started — no badges

   7 areas · 12 trainers · Rival Blue (Bulbasaur), Rival Blue (Charmander), Rival Blue (Squirtle)

2. Part 2: Beat Brock — Pewter City Gym, badge 1

   17 areas · 74 trainers · Rival Blue (Bulbasaur), Rival Blue (Charmander), Rival Blue (Squirtle) and 1 more

3. Part 3: Beat Misty — Cerulean City Gym, badge 2

   1 area · 3 trainers · Misty

4. Part 4: Got HM01 Cut — S.S. Anne

   13 areas · 118 trainers · Rival Blue (Bulbasaur), Rival Blue (Charmander), Rival Blue (Squirtle) and 1 more

5. Part 5: Beat Lt. Surge — Vermilion City Gym, badge 3

   1 area · 3 trainers · Lt Surge

6. Part 6: Beat Erika — Celadon City Gym, badge 4

   1 area · 8 trainers · Erika

7. Part 7: Got the Poké Flute — Pokémon Tower

   8 areas · 49 trainers

8. Part 8: Beat Koga — Fuchsia City Gym, badge 5

   11 areas · 42 trainers · Koga

9. Part 9: Beat Sabrina — Saffron City Gym, badge 6

   1 area · 8 trainers · Sabrina

10. Part 10: Beat Blaine — Cinnabar Island Gym, badge 7

    1 area · 8 trainers · Blaine

11. Part 11: Beat Giovanni — Viridian City Gym, badge 8

    7 areas · 27 trainers · Elite Four Agatha, Elite Four Bruno, Elite Four Lance and 5 more

12. Part 12: Beat the Elite Four and the Champion

    1 area

It also doesn't say when Kanto Underground Path opens up, so it is in no part above; it has its own route page.

What you can catch at each checkpoint · Every area