Castelia City is a huge city in southern Unova with countless skyscrapers piercing the clouds, several piers which contain many boats, and also has the region's third Gym.
As you might expect from such an expansive city, there are many areas to explore, with notable buildings including the Battle Company, GAME FREAK, and the Casteliacone stall.
When you travel through Castelia City, the camera will zoom in and out, and when you leave, the camera will show you Castelia City from a distance.
Unnamed Oceanside Street - The street overlooking the ocean houses the Pokémon Center in the east. Further along you'll see the Battle Company building, where the employees are waiting to challenge you. Also on this road is the Passerby Analytics HQ; if you pop in they'll give you more surveys for your C-Gear.
Castelia Street - The Unova GAME FREAK Head Quarters are located here, where you can meet the game director and a few other developers. One of the game designers will challenge you to a match after you've defeated the Elite Four. In the building opposite the GAME FREAK HQ, a lady will give your Pokémon a massage, making it more friendly towards you.
Central Plaza - Has a grand fountain. When you find the three dancers around the city, they'll be here.
Mode Street - The famous Casteliacone is sold here, but as it's extremely popular it's sold out every day apart from Tuesday; You have to go early Tuesday mornings if you want one, and only once a day. In Studio Castelia, an art gallery, a harlequin will give you a berry if you show him a Pokémon of the correct type.
Narrow Street - Has Café Sonata. A shady man lurking behind the bins will give you the TMFlash.
Castelia City gets its name from the Latin term castellanus, which means of a castle or of a fort. That term is used in conjunction with several varieties of clouds, such as the Cumulus castellanus, the Cirrus castellanus, among others.