Under the cycling road, to the right. You have to know surf.
New Mauville is located on Route 110, underneath Cycling Road.
New Mauville city
new mauville after you get a key from Wallace
step on a button in front of the generator
After a certain point in the game, you will see Watson standing in the middle of Mauville outside of his gym. If you talk to him and agree to help him with his problem, he will give you the key to New Mauville.
New Mauville Once you have surf, Plusle and Minun North of Slateport, Pikachu I think in the safari zone, and electrode in the team aqua base
You can get a Thunderstone in New Mauville and by trading a Yellow Shard to the Diving Treasure Hunter on Route 124.
Mauville City But you have to beat the city's gym leader before you can turn off the generator in New Mauville City
idk its just closed there really is no reason wattson will give u the key if u help
first,talk to the gym leader at mauville(he will be out side the gym)then he will tell you about new mauville,then he will give you the basement key.second,you need to go to the river in front of the trick house and use surf and go forward.you will see a cave.go in and you are new mauville!
From Mauville City, go south, you'll meet the Fisherman. Surf and keep to east. Then, you reach the New Mauville.
First beat the Mauville Gym leader, Wattson.