The way to Lake Acuity and Snowpoint City is long and treacherous. You need to travel through the northern part of Mt. Coronet and head north. Make sure to bring Pokemon with Strength and Defog at the very least, though Surf and Rock Smash are also recommended! As you get through Route 217, MAKE ABSOLUTELY SURE YOU PICK UP HM08 ROCK CLIMB! You need it to get through the game!