Frankfurt in ONE Unhurried evening
 

Spending my last night next May in Frankfurt so that I can catch an early morning plane.
Will have just finished up 7 nights in Bamberg with multiple daytrips.
Arriving Frankfurt about 3-4 PM.
Looking for a calm and unhurried stroll + dinner and perhaps one or two sights, all not far from the Bahnhof.
Too late in the day for museums.
What would be your ONE must-see sight that is quick to reach?
Not interested in bars or pubs as up early for the next gruelling day of travel back to USA.
I realize that Frankfurt requires MUCH more time to truly appreciate!

In May, the daylight hours will be quite long, so you could have a really good walk around the city. The center of downtown Frankfurt as well as the Römer / Alt stadt areas is about a 15-20 min. walk from the Hauptbahnhof. Walking along the river would be a pleasant thing to do. With-out knowing what your interests are, it is hard to say what is the #1 thing to do or see, so will list my top suggestions and you can pick and choose, though many of them can be seen in just a couple of hours walking around. Depending on the day of the week, you might also want to visit one of the Farmers Markets held in the downtown area, Thur. Fri. and Sat.

* Karmelite Cloister - Jörge Ratgem wall paintings, done early 1500's. Get the English audio guide.
* Jewish Holocaust Memorial Wall
* Alte Oper
* Römerberg, with the Kaiserdom, Alte Nikolai (built 1290), and the Book Burning Memorial
* Klein Markt Halle, wonderful indoor produce market
* Palmengarten
* Bethmann Park and the Berger Strasse in Bornheim
* Main Tower, stunning views of Frankfurt and the Taunus mountains
* Deutsche Ordens Church (Teutonic Order of Knights) built 1309

Again, depending on the day you are here, there may very well be a fest going on in the downtown area. Also, many of the museums stay open late one day a week. Worthwhile for the Städel, Liebieghaus, Schirn, Applied Arts or Museum of Modern Art.

You might want to consider staying in Mainz instead. It is west of the airport instead of east as Frankfurt is, but is in some ways an easier transit. You can get decent hotels right by the Mainz train station at a good price (have a look at www.hotels.de ). The Altstadt has character, and is a great place for a farewell meal and wine samplings. The town is easy to negotiate, both more compact and easygoing than Frankfurt, and the S-bahn and R trains run about every 10 minutes, taking between 21 to 27 minutes direct to the Frankfurt airport.

Late reply, but as you will not be in Frankfurt until May you might like to check out the Museum opening hours in Frankfurt. Many are open until 8 or 9 pm on at least one night a week.
See http://iguide.travel/Frankfurt/Sights/Museums
The collections are stunning and I am assuming you are interested in museums as you mention you will be too late to visit any. But, not necessarily! Many also have cafes though you would need to check they are open also.

Thanks everyone!
Have already been to Mainz and thoroughly explored it on a past trip.
Have checked the museum hours---seems that Wednesday is the late day for most (we will be there Thursday evening :-().
Looks like will will head to the Altstadt after checking into the hotel, to see the Roemer, Dom, Hauptwache and do dinner.
We have not yet pinned down our actual flight, so I am looking at possibly delaying the trip home by one full day. That would give us the evening AND ONE FULL DAY too! If that gloriously happens, we will use the second and full day to visit respective museums of interest (and I would like to see the Jewish Memorial Wall since I minored in Jewish Studies so many years ago!)
Now if the darn airfares would only cooperate!

The Stadel is open till 9 pm Thursdays and is one of the best.
See
http://www.staedelmuseum.de/sm/index.php?StoryID=1230
Enjoy!

Bookmarking for our June trip - probably will have an entire day in FRA prior to our return flight, so these are good suggestions.

I noticed that old Sachsenhausen is not on your list, Mainhattan girl, for the one night; We are going in June too and had thought to walk from the railroad station to Romer square and then via Saalgasse (postmodern buildings) across the bridge to the Klappergasse area for dinner. What is your opinion of that, and do you have any restaurants to recommend that don't serve heavy greasy (yes I know, its German food) meals?