<p>I absolutely second what xiggi said. Except we stayed at the newish Hilton Garden Inn which was attached to the terminal, so we did not even have to go outside of the airport:</p>
<p><a href=“http://m.hilton.com/mt/hiltongardeninn3.hilton.com/en/hotels/hesse/hilton-garden-inn-frankfurt-airport-FRAAPGI/index.html”>http://m.hilton.com/mt/hiltongardeninn3.hilton.com/en/hotels/hesse/hilton-garden-inn-frankfurt-airport-FRAAPGI/index.html</a></p>
<p>Took the train into the city and back (with the beer and sausages and tasty kraut packed securely in our bellies). 
There is also a shopping center attached to the airport. </p>