411 REFERENCE · Wikibooks
A Traveler's Guide to the World of Pokémon/Hoenn/Rusturf Tunnel
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
Rusturf Tunnel is a tunnel between Rustboro City and Verdanturf Town. It has been featured in several different places, including the anime and some of the video games.
First, a member of Team Aqua (Sapphire/Emerald) or Team Magma (Ruby) will steal Peeko, the pet Pokémon of Mr. Briney, a ship captain.
After, you have to use Rock Smash to join two lovers. The man will give you the HM Strength. The only Pokémon obtainable here is Whismur.