After ignoring “Mainhattan” for years, I decided to do a whirlwind tour of the old town immediately after arriving on overnight flight. With just a few hours to spare, here's what I found is the best way to "do" Frankfurt in a flash.
Take the airport train to the Hauptbahnhof, catch either the U-4 or U-5 subway and exit about 3 minutes later at Römerberg. You can alternately walk up Kaiserstraße, which takes about 20. After exiting you can go south a few steps and reach the river Main for a quick view, then move towards the red tower of the Kaiserdom and the Römerberg, Frankfurt's historic heart.
The first thing to remember as you're standing in the square is that pretty much everything around you was rebuilt after Frankfurt was flattened during World War II. But, don't let that spoil the view of the half-timbered buildings and the town hall.It was here that the city's first trade fairs took place in the 13th century.
One of the most important structures here is the Paulskirche, considered the birthplace of German democracy, It was here that the first freely elected national assembly met in 1848 and drafted the first German Constitution.
Modern architecture echoes the old pre-war designs on Saalgasse. At the end of Saalgasse you'll find the Kaiserdom (St. Bartholomew's Cathedral), where ten Holy Roman Emperors were crowned. In front of the cathedral are some Roman ruins as well as a monument to Charlemagne, who gave the city it's name. (His Franks could ford the river here.)
Remains of the city's former Jewish ghetto (15th to 18th centuries) were uncovered to the east of the cathedral. Frankfurt once had Germany's second largest Jewish community, which can be explored at the Juedishes Museum at Untermainkai 14-15.
Heading back westward you'll notice the skyscrapers above the rooftops as you pass by the birthplace and boyhood home of Johann Wolfgang von Goethe, Germany's most famous literary figure. The Goethe Haus has been refurbished in period furniture and artwork across several floors, and includes the desk where Goethe wrote "The Sorrows of Young Werther".
With more time you can explore the city's many museums and the restaurants in the charming Sachsenhausen district south of the river. But, for now, you're back at the station with the best of Frankfurt tucked safely under your belt.