Is there a hotel or other facility INSIDE Beijing Capital Airport where we can sleep?

My question is the same as many people appear to ask: We'll be flying to UlaanBataar through Beijing, arriving at midnight and leaving at 8am. If we stay in the airport, we don't need a visa, but if we step out, we do. Is there a hotel or other facility INSIDE the airport where we can sleep comfortably?

Thank you.