How would a hamster escape to outside as in out of the house?

I lost a hamster for almost a week now. I have a two story house and checked everywhere for her ( hamster) but can't find her, I leave out treats in every room, and I check everyday if it did eat it but no luck. And there's no way she can be in the vent because it's up in the ceiling. So everybody tells me she probally escaped outside. Like how would she get outside?