the elite 4
All you have to do is train your Pokemon or have a Pokemon with a good ice move
EVERYWHERE!
a place with strong Pokemon
easy route 26 kanto johto
Seven island at sevault canyon.
Well, you need to train your Pokemon! Get your Pokemon to a high level, and make it learn good moves. Head to the Pokemon Center to buy all the medicines you think you'll need. (Ex: Potions, Super Potions, Hyper Potions, ETC). Train, Train & Train your Pokemon to succeed!
victory road is a pretty good place
rt.224
anywhere.
A good place to level up higher leveled Pokemon is through gym leader rematches.
the elite 4 or the places with the highest lvl wild Pokemon in them
Nowhere.