We are coming from Denver to Geneva with a 5 hour layover in Frankfurt. I have been in Germany 5 or 6 times but have never left the airport. I would love to see something, even if it is just a quick coffee at cafe. Is there a fast train into the city? Any suggestions?
Yes, there is an S-Bahn that gets you into the city in 11 min. If you stay on for 2 more stops, it lets you off at the Hauptwache. This is a 5 min. walk away from the Römerplatz or old town square, cathedral, river, etc. If there is more than one person, buy a "gruppenkarte" which is about 14 €. This will cover you going into town and coming back and is good for up to 5 people. If you want to spend the money, a taxi will run about 30-35 € depending on traffic, etc.
Hopefully, your flight will land early and you will have even extra time. Since you are flying somewhere else in Europe, you need to be back at the airport around 1.5 - 2 hours early to check back in. Take a look around at the airport when you arrrive, if it looks packed, allow a bit of extra time. Summer can be like that. Or if it is not so packed, well, you get through the lines quicker.
Thank you for your help!