From Bulbapedia, the community-driven Pokémon encyclopedia.

Johto's Battle Tower is located on Route 40, west of Olivine City.

It only appears in Pokémon Crystal and is separated from the route by a gatehouse. After winning seven battles in a row, the player will be awarded with five Irons.

Rules

• Trainers may only use 3 Pokémon
• They must all be less than or equal to the level challenged (which are in intervals of 10)
• They cannot hold the same item
• Trainers can't use items

Levels

Pokémon can be as high as the level chosen, but no higher. If the game is turned off during a challenge without saving, the challenge will be declared invalid.