First, you'll need a Pokemon that can use the 'surf' move. Once you've
grabbed one from storage, go to Dendemille Town and then leave via the
bridge located in the north part of the town. You'll find yourself in
the snowy mountains on a path that leads to the Frost Cavern. To avoid
constant battles, feel free to use a Max Repel.
Pass through the cave, heading upstairs through the doorway on the
right. Make further progress and you'll eventually find a small
stream. Next, use surf to reach the other side of the stream. Follow
the path around and head downstairs.
See that big glacier in the middle of the room? Well, that's an ice
rock. Run around until your Max Repel wears off, then level-up an
Eevee while near to the rock. It'll evolve into Glaceon upon
completing a battle
^Amazibg descripton from this Amazing site
Hope I helped:)