Transit visa procedure in Qingdao

I’m flying from US to Seoul via QD and have 14 hour overnight layover in the city. I’ve read that you have to stay in the airport for transit visa, but airport closes at night, so we’re going to nearby hotel. Do we need any type of visa before we leave, or just the passport. Can we get the transit visa if we have to leave the airport and how is that process? What does it cost? Traveling with children, so want to be prepared. Thank you!