City: Castelia City is awesome, it's music is so <3. I also love Opelucid, it's city theme is awesome and how it changes between game version.
Route : Route 10 :o Maybe since because I used to Audino Train there when I was desperately levelling up my party for Elite Four (old).
Bridge :Skyarrow Bridge, Marvelous Bridge and the Bridge in Entralink (The way you changes character when entering someone's world is awesome <3