United and Star Alliance airlines offer a fare from Chicago to Frankfurt that is down to $536 round trip for November 22 to December 15 departure dates. The catch is the fare drops to $536 only if you stay 7 days or longer. This deal is available on several different Star Alliance airlines. United and Lufthansa offer nonstop. Air Canada, LOT and Swiss will connect you via hubs in Canada, Warsaw and Zurich. LOT offers short duration trips at $609 for some dates.
Departure Dates: This is a limited window sale with ticket prices at $536 November 22 through December 15 and only for 7 day stays or longer, like Nov 24-Dec 1. Prices are $558 for 6 days (Nov 24-30); $609 for 3-5 days on LOT. Fares are in low to mid-$600s for earlier November departures.
Google Flights Chicago ORD – Frankfurt, Germany FRA
$536 round trip on several Star Alliance airlines Tue Nov 22 – Wed Nov 30
SkyTeam ($887) and Oneworld ($1,204) airlines have not touched this fare yet.
Lufthansa Airlines ticket from Google Flights
$535.20 round trip Tue Nov 22 – Wed Nov 30
If you can leave by December 15, you can come back nearly any date over the Dec-Jan holiday months at same low fare.