My daughter and I are stuck at the part with the post office and what looks..

You have to enter one of the stores. When you get in there there will be spiders, kill them and use shaggy to zip line to the top. Grab a snowball and then jump down. There is a fireplace that is lit and it is blocking scooby's door. Throw the snowball at the fire, this allows scoot to go through the door. Then you will see a short cutscene of a door unlocking upstairs. Use either shaggy on his zip line or scoots door to get up there. Then exit the door. You will find yourself outside and on a balcony. Jump on top of the roof and at the very edge you will see a medallion. Grab it and enter the next are you have been trying to reach. That giant pile of snow will only disappear after you have to track down the yeti and he pushes through it. There will also be a small store that the snow was blocking. I believer there is some sort of treasure there. Hope this helped!