Pokémon Yellow: Got the Poké Flute — Pokémon Tower
What opens up at this point in the game, and everything you can catch by now that you couldn't before.
✓ Mr. Fuji gives you the Poké Flute once you rescue him at the top of Pokémon Tower, where the ghosts need the Silph Scope, found in the Rocket Hideout under the Celadon Game Corner. The flute wakes the Snorlax blocking Routes 12 and 16, which is the way south to Fuchsia.