After you go north through Route 4, you find Nimbasa City. The supermodel, Elesa, has a pokémon gym here. She built a new one, so she isn't in the roller coaster building anymore.
Learn to Fly
Before you start looking around Nimbasa, go west to route 5. Bianca will meet you and give you HM02 Fly. Teach Fly to a pokémon and you can fly to any destination you have visited in the past.
Bianca will also teach you about grottoes, which are hidden areas in the trees where a pokémon hides out. She shows you a nearby grotto where a Minccino is hiding. Talk to it to start a pokémon battle, where you can try to catch it.
Go to the left of the Nimbasa pokémon center to find a hidden Thunderstone.
There is a guy in the pokémon center who gives you red shards.
Go into the house south of the clown and talk to the Ace Trainer upstairs to get a Sun Stone.
In the house to the left of that, the old lady upstairs will give you a soothe ball if it looks like you and the pokémon in your first slot get along.
Go southeast through the colorful gate to reach the amusement park. To the south of the gate, southwest of the flowers, there is a "Dropped Item". Pick it up and you will get an Xtransceiver call from "Chr... I mean Curtis!" The item that you find is his lost Xtransceiver. He is using an old Xtransceiver that uses no video. He's busy with work, but he will come pick up his Xtransceiver when he can.
There is a hidden Revive in the trash can to the right of the roller coaster.
You can battle the guy in front of the ferris wheel. It's Clerk ♂ Augustin. He has a level 24 Tranquill. Afterward, you and Augustin will ride the ferris wheel. It's all old and creaky. After, Augustin says his company owns the ferris wheel, but they're thinking of tearing it down because it's unpopular and there are safety concerns. But you can go on ferris wheel rides if you want.
There is a Parlyz Heal to the right of the Audino statue in the east side of the amusement park.
Talk to the sport guy at the east gate of town to get a Macho Brace.
The Nimbasa theater is pretty much the same as in Pokémon Black and White. See the Musicals at Nimbasa section for more information.
There is a girl on the right side of the theater who gives you TM49 Echoed Voice.
If you go to Elesa's gym, Clyde is at the door and says that Elesa is not there right now. You have to go to the roller coaster building to the left of the gym.
Take the rightmost rollercoaster when it arrives, then press down to exit when it stops. Press the switch to the right. Get into the coaster and go to the next stop. Press the switch up above and go into the coaster above. A trainer comes out: Rich Boy Rolan. He has a level 24 Blitzle.
After defeating Rolan and riding the roller coaster he came out of, exit at the bottom right. Press the purple switch and get into the coaster on the right. Lady Colette comes out and sends out a level 24 Flaafy. Get into the coaster that Colette came out of and exit at the next stop.
Talk to the girl at the top. She gives you a Parlyz Heal. Step on the switch to the left of her, then get in the coaster and exit the building.