Main, Germany

You can take a one-hour boat trip on the Main river, which is a great, quick, non-stressful way to see everything along the riverbank.

I've picked up American friends for a similar "day trip" just a couple of weeks ago. Here's what we did. There are lockers on the arrivals area in case you need some.
Take S-Bahn from the airport to Taunusanlage (about 20mins ride). Alight there and you're just between the headquarters of Deutsche Bank and European Central Bank. Walk thru the park towards the Opera building (you can spot it from there) and have a coffee on Opera Square or in the pedestrian zone that starts just East of it.

Then follow that shopping street all the way until you get to the big "Kaufhof" department store. Right behind it is some kind of vertical shopping mall called Zeilgalerie. Take the elevator all the way up and enjoy the view from the roof top viewing area.AAfterwards walk down the little street just across from Kaufhof (Liebfrauen St.) until you get to an open square. When reaching that square there is an opening [...]

of that square in the 10 o'clock direction. Walk thu it if you want to stroll thru the market hall with its local and regional specialities. You can sample a lot of the food there or just enjoy the atmosphere. Leave that hall thru the same entrance you walked in and go back to Liebfrauen St. Follow it downwards. PS: You can visit the church that also comes with some kind of convent, too, if you want.
After crossing the big street you're outside St. Paul's church, the venue of the very first German democratic parilament in 1848. Obviously that attempt to unite and democratize Germany failed and ended in the 2nd Reich or empire. Different story.Then continue across the tram tracks to Römer sq., Frankfurt's main square. It's also the venue of the annual Christmas market. The town hall is on the right hand side. But turn left for now and walk to the big cathedral just behind the square. It's the more than 1,000 years old emperors' cathedral where most emperors [...]

of the Holy Roman Empire of German Nations were crowned. There are some geniune roman remainders just outside the church. Walk back to Römer qu. and continue downwards to the riverfront. Cross the river using that old iron bridge in front of you and then turn right (westbound) and walk to the next bridge. Cross back to the other side and visit the Nizza, a mediterranean garden named after Nizza (Nice) in France. You could have a snack at the beer garden there.Then leave the riverfront, walk towards that giant €-Symbol which is just outside the European Central Bank's building. From the tram station there (Willy Brandt Platz) Take westbund tram line 11 towards Höchst Zuckschwerdstraße. Take tram all the way to the final destination. Ask driver which building Bolongaro Palace is. Walk around that palace to the Main's riverfront (all the way down), turn right and walk for a few 100 yards until you see the big castle. You can enter it thru the 1,200 years old [...]

customs tower right after the playground. You're now in old-town Höchst on the market square. You're facing two restaurants with outside seating. Take the left-hand side one (I think their sunscreens are blue) and ask the waiter for a sampler of traditional Frankfurt food. Drink a glass of Cider-spritze (Apple Wine Schorle) with it.
From that square it's about a 20mins taxi ride back to the airport. Enjoy Frankfurt!! [the end]