Is there a recommended activity if I have a 22-hour stay at FRA airport?

I am arriving at around noon on a Monday, then leaving around 10AM the next day.

I plan on staying at one of the hotels near the airport and on google maps, it looks like there are a bunch of them just 4km away. I plan on checking in very early the next day as I would like to hang out in the lounge. So basically, I have an afternoon and the early evening for a FRA 'stay'.

Any suggestions?