Go forward, up the steps into the city itself. At the junction, take the path west. Continue until you reach the Pokemon Center. Feel free to heal yourself and do whatever else you need to. Make sure to talk to the man to the right of the Nurse's counter, as he'll give you Red Shard x10 . Now it's time to explore Nimbasa City!
Attempt to enter the building to the left of the Pokemon Center and a girl will come out and stand in the doorway. This building's the Battle Institute, but cannot be entered until you've beaten the Champion. For now, go around so that you're behind the Pokemon Center.
Now run down to the left side of it. You'll notice that your Dowsing MCHN is picking up a reading. Pick up the Thunderstone to the left, next to the Pokemon Center. Then head north and enter the building to your left, the one at the end of the street.
Go up the stairs onto the second floor. Talk to the old woman and if the first Pokemon in your party is happy enough, she'll give you a Soothe Bell . Exit this building and enter the one next door. Go up to the second floor of this one and talk to the blue-haired guy. He'll give you a Sun Stone .
Now go back to the Pokemon Center and take the path east. You'll see a person standing in front of a building to the north of the path. The person is the main character that you didn't pick to play as (ie. the one of the opposite gender).
He or she is standing off against two men, one in white and one in black. Go up and talk to the person. They'll ask if you wish to help him/her fight these two men in a 2-on-2 battle to gain access to the Subway. If you're willing, answer 'Yes' and the battle will soon commence.
Double Battle: Subway Boss Ingo and Subway Boss Emmet
The character you're teaming up with has the following party:
If Snivy was your starter
If Tepig was your starter
If Oshawott was your starter
After beating the subway bosses, they will leave. Then your partner will give you the Vs. Recorder ! You can use that to record online battles and such, so it's nice to have! Finally, he or she will enter the Battle Subway, also known as Gear Station.
Head back to the Pokemon Center and take the path north, over the bridge. You'll see Big Stadium immediately north of you when you cross the bridge. You can enter the Stadium and battle trainers once per day but not during event hours (which vary from day to day).
There are always at least three battles available, usually against the sportspeople. The type of sportsperson depends on the day, and the level of their Pokemon is dependent on your badge count. Small Court , which is next to Big Stadium functions in the same way, but has different sports and different event hours.
Check the Essential Areas section near the end of the guide for information on which trainers you can battle on which day with your current badge count.
East of Big Stadium is the Musical Theater , where the player can partake in Pokemon Musicals. You can only join in after defeating Elesa however. There is a TM in here though. Walk to your right and talk to the lady along the back wall, next to the Vending Machines. She'll give you TM49 - Echoed Voice .
If you continue west along this strip, you'll reach the gate leading to Route 5 . If you're looking to train before you face Elesa, this city's gym leader, this is one of the places to go as there are trainers that should be around your level. Meanwhile, heading east will take you to the gate to Route 16 .
Route 16's trainers are about the same level as Route 5's, but there are many more of them and the area leads into Lostlorn Forest, where even more trainers are, as well as some nice Grass- and Bug-types. If you talk to the Black Belt at the gate to Route 16, he'll give you a Macho Brace , so make sure you collect that off of him.
The only thing left to check out is the amusement park , which contains the Rondez-View Ferris Wheel, the Old Nimbasa City Gym and the new Nimbasa City Gym. Go and enter it (it's near the entrance to Nimbasa City). As soon as you enter, move south, off of the path.
You'll find a Dropped Item . Well, we must find who the owner is! That will come later, though. For now, return onto the path and follow it east. Just past the Old Nimbasa City Gym are two Vending Machines. Next to them is a bin. Look in it to find a Revive . Follow the path along, past the Ferris Wheel.
When the path turns north, continue moving east, onto the grass. You'll see a giant Pokemon statue. To the right of it is an item. Move over and grab it to find that it's a Parlyz Heal . Now move back to the Ferris Wheel.
The Rondez-View Ferris Wheel is another daily event. Each day you can battle the trainer standing at the base of the ferris wheel once. The trainer you battle each day depends on gender and on what season it is. The possible battles are as follows:
If Main Character Is Female
Trainer Battle: Clerk (Summer)
Trainer Battle: Hiker (Autumn)
Trainer Battle: Guitarist (Winter)
Trainer Battle: Dancer (Spring)
If Main Character Is Male
Trainer Battle: Nursery Aide (Summer)
Trainer Battle: Clerk (Autumn)
Trainer Battle: Beauty (Winter)
Trainer Battle: Lass (Spring)
To battle the trainer, talk to him or her and answer 'Yes' when asked. The battle will commence. After defeating a trainer, you will take a ride on the Ferris Wheel with them. Afterwards you'll be free to go on your way!
As a suggestion, we'd recommend first tackling Old Nimbasa City Gym, then taking on Route 5 and Route 16 before finally challenging the New Nimbasa City Gym. This will allow you to train up to a standard that's able to defeat Elesa, the gym leader.
Oh, but before that, you should check out the nearby Anville Town if you have some spare time and haven't already been there.