Thanks. 
I’ve had a couple of long stopovers in Frankfurt before, so I have an incredibly basic (and not particularly favorable) sense of the city. I’ve only ever left the airport once, after an early morning touch-down en route from Israel to San Francisco.
We caught a cab to the city center and kindly requested that the driver take us to the best local breakfast place in town; only requisite was good quality GERMAN food. He drove us to a McDonald’s. I’m not kidding. We spent the next 30 minutes or so rushing through the streets, trying desperately to find a place - any place - that was open. It was roughly 8 AM and we had approx. one hour before we had to cab back to the airport.
We finally stumbled onto a traditional looking deli that appeared to be slingin’ homemade sausages with quality cheeses and freshly baked bread. Great, we thought, and then… CASH ONLY!
We spent the remaining half hour of our time in Frankfurt running around town trying to find an ATM that was compatible with our cards… we had a stockpile of plastic in our pocket: Visa, AmEx, MC, Debit, you name it. Not one single ATM in that godforsaken city worked! We tried convenience stores, banks, we even ran into an int’l travel agency for help. Nobody spoke English, not even in the travel agency which was in the lobby of a youth hostel. We were not having any luck. Miraculously, just as our tireless efforts and lofty breakfast aspirations began to disintegrate, we managed to somehow withdraw cash, literaly as the ticker was winding down to zero hour.
We bought some stupid frankfurters and cheese and ate it in a taxi on the way back to the airport. That’s my one and only experience of the city, and yet somehow, despite it being colored by the extremely aggravating circumstances, I don’t think my impressions would have changed very much otherwise. I know it’s an unfair generalization but in my very short time between transit, I found what little we saw of the city to be kind of ugly and depressing; it felt really down at the heels. The people were not the friendliest we’ve encountered in our travels either, but I suppose our limited time and exposure was hardly enough to form a balanced opinion. I’ve not read many enthusiastic opinions from others though.
Anyhow, all that to say… I actually canceled and rescheduled our return flight a couple of weeks ago, gladly incurring a $75/person fee, just to book a later 7:05 pm departure so that we could fit in one more meal in Venice!! 
Who wants to leave the most romantic city in all of Europe to spend an afternoon in Frankfurt?? Haha Unfortunately, I booked our Frankfurt hotel on an earlier prepaid rate, before rearranging our itinerary, so while it would now make way more sense to check into an airport Sheraton, clock out, and leave the next morning… we still have to drive into the city to spend the night. That’s all we’ll be doing though. I’m milking every last second that I can get out of Venice… we’re looking at Frankfurt as a place to sleep for the night and nothing more. We’re arriving after 9pm so we’ll most likely just check into our hotel, reminisce about our enchanting week in Venice, and not leave the room again until it’s time to leave for the airport.