Yes, you have to complete the game, ie, defeat the elite 4 and the champion. Doing so will unblock many exits, letting you go on Skyarrow Bridge, into Twist Mountain, to Icirrus City, etc.
follow the road in Pinwheel forest and enter the white thingy
In Black 2 as well as White 2, Skyarrow Bridge opens up once you've beaten the Elite 4 and the Champion.
Pinwheel Forest is West of Nacrene City and South of Skyarrow Bridge.
You can finished the game, but now you can visit southeast Unova by going across Skyarrow Bridge.
The gamefreak building is in Castelia City. It is on the first road from where you enter from Skyarrow Bridge.
It is West of Nacrene City and South of Skynarrow Bridge.Pinwheel Forest is West of Nacrene City and South of Skyarrow Bridge.
You need to start with Oshawott. At the dreamyard a guy gives you Pansear, then at Castelia city right before the gate to Skyarrow bridge you go down talk to a scientist and answer pansear
trade with 50 people. Next, you go to castielia city which is next to skyarrow bridge and route 4. talk to the man next to the union room. he will give you a master ball.
Once you enter Castelia City from Skyarrow Bridge, go down the 1st pier that you see. There should be a scientist there. Talk to him. He will give you a choice between 3 stones. Choose the Fire Stone.
There is no Pokemon Center north of Nacrene City. The next Pokemon Center after Nacrene City is through pinwheel forest and across the Skyarrow Bridge in Castelia City. According to the in game town map Castelia City is west past Nacrene City. There is nothing north of Nacrene City.
When you get off skyarrow bridge and enter castelia city go to the very first pier. There will be a scientist giving you an option of water stone fire stone or leaf stone
Tubeline Bridge