First, you have to have beaten the galactic grunt, and make sure you have the HM 'Defog' ( get from tower south of Solaceon town, at the very top ), and a pokemon who knows HM Strength. Get "strength" at the lost tower near hearthrome city. Look for to old ladies. Idk if it's the Elite 4 well lol! Then fly to the Pokemon leauge and use waterfall to get down and go into Victory road. then use rock climb to get down and then go left, up, left and up the stairs. Then go right across the bridge, up and around the block until you see a cave entrance. Go in. Then, go down both sets of stairs and into the other entrance. After that, you'll see that it'll have become foggy. Also, you'll be teamed up with someone named Marley.

Then just go through victory road and you'll be on your way to route 224

http://wiki.answers.com/Q/How_do_you_get_to_Route_224_on_Pokemon_Diamond