Nacrene City is an old city in eastern Unova, located between Route 3 and Pinwheel Forest. It's peculiar cityscape was made up of abandoned textile factories and century-old warehouses, until enterprising young artists began using them as studios. This was essentially the beginning of the city, and it is still known as the city of art to this day, attracting many creative artists and poets. A disused railroad lies in the south of the city.
The second Gym of the region, which doubles up as a fossil museum, is found here. There are a few other notable places to visit too; such as Café Warehouse, which has a Soda Pop special on Wednesdays; Loblolly's studio, where Loblolly designs furniture for you to use in the Dream World; and a warehouse shop selling battle items.
When you first arrive in the city, Cheren is waiting to talk to you about the Gym, and advises that having a Fighting-type Pokémon will give you a big advantage. He kindly hands over a few Chesto Berries as well. However, when you head to the Gym you'll find N, who shares his opinions on Pokémon before challenging you to a battle.
After defeating him you can go inside and check out the museum, with Leona's husband, Hawes, giving you a guided tour. Amongst the curiosities are a Dragon Skull, an ancient round stonethat was buried in the desert, and a meteor that has a space virus attached to it. The latter can be used for changing Deoxys's forme. You can also have fossils restored here by the woman behind the right counter.
Once you've beaten Lenora, Hawes runs in and informs you both that Team Plasma have taken over the museum. Team Plasma steal the Dragon Skull and vanish in a puff of smoke. You and Lenora chase after them and bump into Burgh, Cheren and Bianca who offer to help after hearing what's going on. Cheren and Bianca stay to protect the museum whilst you and the others search for Team Plasma.
Once the player has defeated the Champion, the areas past the Skyarrow Bridge are accessible. Once you reach Nacrene City, you can go to the Nacrene Museum, and a text box will say that a mysterious presence can be felt, and if you'd like to search around. If you say yes, Uxie will appear. It will be blocking the entrance, and you can try and capture it, or defeat it. If you say no, you can continue on to the entrance of the museum. Hawes will greet you, and soon Lenora will appear. She retreats back to her study, and you can go back into the old gym, and go to her study. She will deliver a short speech, and give you the choice of the Plume Fossil or the other fossil. In the cafe a lady will give an item called Grubby Hanky and on Thursday you can give the Grubby Hanky to this dude with a Patrat.