Route 34 is a route south of Goldenrod City and north of Ilex Forest. In the route, there is a Pokémon Day Care, where the player can leave their Pokémon to level up, as well as breed almost any of their Pokémon with a Ditto, resulting in an Egg.
Speaking to this lady gives the player a TM12 (Sweet Scent).
The gate to the Ilex Forest (Gen II)
In Pokémon Crystal, when registering Picnicker Gina to the PokéGear, she can sometimes give the player a Leaf Stone when she calls.
Entrance to the Day Care Center
There is a hidden Super Potion by the pond at the Day Care Center's front yard.
In Pokémon Crystal, when registering Camper Todd to the PokéGear, there might be a sale at the Goldenrod Department Store rooftop when he calls sometimes.