The Underground Path is a subterranean building linking routes 5 and 6 in Kanto, and the only way to get to Vermillion City from Cerulean City until Saffron becomes accessible later in the game.
Inside the Route 5 (north) end, the player can trade a Nidoran to a little girl for a Nidoran of the opposite gender. The received Pokemon is holding a Tinymushroom.
Multiple invisible items can be found on the floor inside:
- Antidote: One square below the top stairs and one square away from the right wall.
- Paralyze Heal: Two squares away from the left wall on the very first blue line heading south.
- Awakening: Against (but not inside) the left wall near the center of the blue section.
- Potion: One square away from the right wall on the first red line heading south.
- Ether: Two squares away from the left wall near the center of the red area.
- Ice Heal: Four squares south of the last red line against the righthand wall.
- Burn Heal: One square above the lower set of stairs and one square away from the left wall.