We're almost done with Castelia City. From the Battle Company building (which is due west from the Pokemon Centre) go a few paces west until you're just past the next lamppost and just before the entrance to the next street. At this point, head down towards the dock.
Talk to the woman wandering around here to receive the Destiny Knot . Exit the dock, and enter the street just to the left of it.
This place is actually a narrow alley. Casually make your way ahead. You'll suddenly get stopped by a rather random shady-looking man that's hiding behind a dumpster. He'll randomly give you TM70, Flash , before letting you go on your way.
Not too far away you should notice a cafe here too. Be brave and enter it. Sonata Cafe doesn't have a lot to do in it, but you can grab a free item. Talk to the man at the counter and he will give you some Moomoo Milk . Exit the cafe and head for the far end of the alley.
Central Plaza and Beyond
You'll now be back in the area with the fountain. Move over to the fountain and talk to the bald man standing next to it. If you do, you'll unlock one of the Funfest Missions called Train with Martial Artists ! How lovely! There are also Vending Machines north-east of the fountain where you can buy drinks that heal your Pokemon.
Once you're done, enter the street north of the fountain. Move down the street and enter the first building on your right. Talk to the man guarding the elevator and reply with the top option ('Yes') when asked if he can search you. Once you're searched, you're free to enter the elevator.
Take the elevator to the 47th floor. It's a party! Speak to the woman in the top-left corner here and she'll give you TM45 which teaches Attract . There's nothing more to do here besides chat to foreigners, so simply leave the building. Enter the building on the opposite side of the street.
Talk to the bald man near the counter. He'll give you an Amulet Coin . Exit the building and enter the second building on the right of the street. Use the elevator here to head up to the 47th floor. In the bottom-right part of the floor is a Charcoal . You can also talk to the man in the centre of the room for information on badges.
Once you're ready, go back outside and head towards the end of the street. There's a Vending Machine next to the gate entrance if you wish to use it. Once you're ready, enter the gate. Move forward a few steps and you'll be stopped by none other than Bianca. This time she gives you the Dowsing MCHN ! What awesomesauce!!
Once she's left you have two options. The first is to enter Route 4, although you can only explore a portion of it at the moment. The second is to return to Castelia City and beat the Gym Leader so that you can explore Route 4 fully. This guide will assume that you're heading back into Castelia, but you can skip ahead a little if you wish.
Anyway, head back to Central Plaza--the area with the fountain--and this time take the western-most street south.
Enter the nearest building on your left. On the bottom floor is the Name Rater! He is the bald man sitting by himself at a table for four. Speak to him and follow the prompts if you wish to rename your Pokemon . Do note that Pokemon you've obtained through trade and that aren't originally yours can't be renamed.
The other two floors that you can visit in this building contain people that have many dialogue options available when you talk to them. One of them includes a woman who will offer one massage per day to a single Pokemon of your choice. This will increase the Pokemon's happiness.
When you're all done, exit the building and continue south down the street.
You will see Clyde standing in front of the entrance to the Castelia City Gym. Speak with him and Iris, the purple-haired girl, to find out that Burgh, the Gym Leader, is currently away and that Team Plasma are involved in yet more antics! Head south, out of the street.
Continue south into the western-most dock. If you wish to, you can speak with the captain of the vessel moored here and get him to take you to Liberty Garden . There isn't much to do there just yet, so you may want to come back later. Once you're done, head back into the main part of Castelia City.
The building to your right has a number of features to do with surveys, greetings and other things to do with online play. If you wish to partake in this, enter and do so.
To continue to the storyline, run towards the right end of the area. Just past the Pokemon Center Iris is waiting for you, telling you that there are Team Plasma Grunts in the eastern-most dock. You may want to heal if you haven't already. Continue. Once you reach the end, follow Iris into the dock.
Iris will tell you that you need to enter the city sewers. Your rival Hugh will then appear. Answer 'Yes' or 'No' to his question and he will promptly run into the sewers himself. It's time to follow him in! Head around and enter.
Castelia Harlequin Hunt
Before heading into the Castelia City Sewers, you may want to partake in the Harlequin Hunt. It's automatically started when you recieve the Bicycle from a Harlequin. You must now find three other Harlequins, speak with them, then return to the original one to receive your reward, a delectable Rare Candy .
The first is in the Battle Company building. This can be found to the west of the Pokemon Center, found just past a street leading north. Head inside and you'll find the Harlequin on the bottom floor, sitting on a seat. Talk with him, then head back out.
The second Harlequin is in the Passerby Analytics HQ . To get there, head west past another street leading north. Just before the next street you'll find the HQ. Head inside and talk with the Harlequin just east of the entrance.
Finally, you'll want the one at the Medal Office . Head for the west-most street, where the Pokemon Gym is and enter the only accessible building to your left. Use the elevator inside to head up to 2F. Then talk to the Harlequin near the elevator on 2F.
Now backtrack to the Pokemon Center. The Harlequin standing in front of the entrance to the street west of the Pokemon Center is the man to talk to to receive your prize. Do so and you'll be handed that Rare Candy ! Once you're done, head onto the Castelia City Sewers!