It's spring on my game tomorrow and I don't want to miss any places that are only visitable in the winter. So what are all the places that are only visitable in the winter?
Twist Mountain(reach different caves, and find different things, like trainers and items) and Iccirus City(double grass and an item)
Hope I helped:)
"Some piles of snow allow you to access areas you can't during the other seasons. This occurs in Route 8, Icirrus City, Moor of Icirrus, Twist Mountain and Dragonspiral Tower."
http://pokemondb.net/black-white/seasons