Pokémon Diamond and Pearl/Route 216

Take the steps on this snowy path, cross the bridge, and pick up the Ice Heal at north end. Follow the bridges west to avoid deep snow. Keep going west, and you'll see a Snowbound Lounge, where you can heal your Pokémon by sleeping in the bed. Go north from there and enter Route 217. There are four trainers on the route. Come back after all HMs are obtained to explore more of the route.