My family and I will have a 23 hours layover in IAD in November prior to flying to FRA. We will arrive at 7pm and will depart the next day at 6pm. Any ideas or recommendations how to spent the layover in IAD or preferably Washington downtown? What's the best way to go into downtown and how to spent the day there? When should we go back to the airport to make it to the international flight?

Thanks for any recommendation