Castelia City (3rd Gym)

The moment you stepped into the city, you will receive bicycle.. Feel free to explore the city, though you probably won't find anything much except a few trainer at the north (near-desert) part.. However, you will notice that there's "rocks" blocking your way..

Once you are done with exploring, head to the first lane from the roundabout..The building on your right is the 3rd gym.. However there's someone blocking you from entering the gym.. Now the current champion, Iris will appear.. She will mentioned that Burgh should be "there".. Go to the rightmost port in the roundabout, the one nearest to the tunnel (tunnel will be blocked by someone till post game)..

You will see Iris here.. She will tell you about the hidden cave.. This cave is Castelia Sewers.. Enter the cave and you will see your rival there.. Here, your rival will tag with you.. As usual, your tagged partner will keep healing you after each battle.. Your purpose here is to find Team Plasma.. They are pretty easy to find in fact.. Just head to the north-west from here.. Though you might want to take this opportunity to explore the area and train your Pokes before going to them.. Once you have beaten the Team Plasma, you should notice there's a hole in front of you.. The cave is Relic Passage, nothing much you can explore here since most of he place is blocked.. You will still be able to battle with some trainers and get some items though.. Now you can head back to the gym..

This gym is a Bug-type gym.. His Pokes' lvl will be about 22~24.. After you have beaten him, heal your Pokes.. Now head north, you will eventually meet Colress twice on the way.. The second time you will have to battle him in the place the "rocks" blocked your way.. The "rocks" Pokes should have moved away before you even battle him.. Now you will be able to proceed to the next city..

However before reaching the next city, you will have to pass through Join Avenue.. You will meet a manager who is too busy to take care of this place, so he left you in charge of it.. The first thing he ask you will be your quote/favorite word.. After that he will leave this place to you.. If you talk to your "assistant", she will ask you what they should call you.. Then she will teach you what you can do with Join Avenue.. Once you are satisfied with this thing, just head north to read the next city..

Desert
For B2: Before reaching Nimbasa City or Join Avenue, you will notice there's a way on your left side.. This will lead you to desert.. While you are still on Route 4, there will be a few trainers here.. You will be able to catch a stationary DW Mandibuzz every Thursday here.. If you go further to left, you will eventually reach Desert Resort after you crossed the tunnel..

For W2: You will enter the desert immediate after the battle with Corless.. There will be a 4~5 trainers here.. On the rightmost building, there will be a healer inside the building.. You can also find stationary DW Braviary there on every Monday.. Once you are done with this area.. Head north, and you will see two ways, one to left, the other to right.. The right will lead you to Join Avenue>Nimbasa City.. The left will lead you to Desert Resort..

In Desert Resort's entrance, there will be a nurse nearby.. So you might want to defeat him/her first.. Unlike BW, this place isn't really important.. You can fight a lot of trainers and get tons of items here with Drowsing Machine though.. If you go to Relic Castle from here, you will noticed that there's dead end after you get to the first lower floor.. Since the structure of the building has changed, you won't be able to go deep here..  So this place isn't compulsory, it's up to you whether you want to "clear" it..