we will have a 5 hour layover in Frankfurt Germany, on our way to Venice. should we play it safe and stay at the airport, or is there a quick, close, and easy
sightseeing jaunt we can take?
There is a thread in the To the West section that is asking the same question (though your layover is longer). You might want to keep an eye on that in case they get any answers there.
There are tons of posts on here (use the Search function) and also over on Trip Advisor about layovers in Frankfurt. Have a look at those to see if they provide the information that you need.
So much to do at the airport - and it's huge... I wouldn't leave the compound. There is a new Bavarian beergarden near the "long distance train station".