Pokémon Ruby and Sapphire/Mauville City

You can do a whole bunch of stuff here, first of all, there is a gym here, which you can battle to get your 3rd badge, in Emerald, you can rebattle this gym after you beat the elite four. You can also get your first bike or you can switch bikes here. There is also the game corner here... Which you can play to win special TMs. Plus, you can get the HM Rock Smash here.

Rydel's Cycles
Here you are given your very own bike! You are given the option of taking the Acro Bike and the Mach Bike. Your choice does not make a major difference, as you can exchange bikes at any time.

Mauville Game Corner
The Mauville Game corner has lots of TMs. This Game Corner has Psychic, Flamethrower, Ice Beam and Thunderbolt! This is the only Game Corner in Pokémon Ruby and Sapphire. There is another Game Corner in Mossdeep City for Emerald users.

In order to play at the Game Corner, you first must acquire a Coin Case. Talk to the lady in the house beside the PokeMart. She will mention Harbor Mail, which needs to be bought in Slateport City. You can take the bike route there and back. Once you give the lady the mail, she will give you the coin case.

Mauville City Gym
This Gym specializes in Electric types. It is recommended that you bring a Rock Type Pokémon like which can be found in Granite Cave in Dewford Town.

Trainers
Beating Wattson wins you TM34, which is. This allows you to use outside of battle, and complete the route between ../Verdanturf Town and continue north along ../Route 111/.