One Night in Frankfurt

"is it a hassle to get into the city from the airport and back out the next day?" No. There is an S-Bahn station (Regionalbahnhof) underground across the street from Terminal 1 (you get to it by going down stairs just inside the outside wall of the hall of Terminal 1). The trip to Frankfurt main station (Hauptbahnhof) takes 11 minutes, and there are other stops in town.

Do stay in town, rather than out at the airport. With a train every 15 min. to the airport and taking only between 11-15 min. to get there, depending on where you are staying, there is no good reason not to be in the city. You can get in lots of sightseeing that evening, or even the next morning for a bit. It doesn't really get dark until quite late, after 22:00, so you can see a lot. What are your travel dates? Since you will be here in June, there will probably be a fest happening, which would be fun to visit. Sitting outside at one of the applewine gardens is always a treat on a summer evening.

I had the same question two years ago for the same reason. We decided to stay in Mainz, per someone's suggestion on the helpline. Taking the train to and from the airport was really easy (I think it was about 30 minutes), and found a room at Novotal hotel for 80 Euros (booked and paid for in advance). Had fun on the train talking to some German guys on their way home from work. They made sure we got off at the right station as there were apparently two train stations within Mainz (which we wouldn't have known). Within walking distance of the train station. Also walking distance to an area with a lot of restaurants.

Thank you for your suggestions. They are what I was hoping for.

"We decided to stay in Mainz, per someone's suggestion on the helpline." Thanks for that suggestion - I was just wondering the same thing for our trip in the spring. We are flying out of Frankfurt but I think I would love to spend our last day in Mainz!