Frankfurt for 2 days

The Staedel Museum is terrific , https://www.staedelmuseum.de/en

A walking tour of Frankfurt is very enjoyable - I learned lots of things I didn't know.

What kind of things are you interested in seeing and when will you be here? There may be events or special exhibits, you may like nature more than history or museums more than markets.

Thank you for your suggestions - a walking tour sounds great since we all like to be outside and hear about the city history!

You can also take a day trip. Two places I have visited that aren’t far arebHeidelberg and Limburg an der Lahn

These are my top things to see in Frankfurt, not in any particular order.

Alt Stadt
Römer & Römerberg
Kaiserdom (St. Bartholomews) climb to the top if you are fit
Alte Oper
Städel Art Museum
Medieval Jewish Cemetery on Batton Strasse (dates back to 1270)
Karmeliter Cloister (wall paintings - 1513-1521)
Klein Markt Halle
Eisener Steg Bridge
Jewish Holocaust Remembrance Wall
Palmengarten & Botanical Garden
Deutsche Ordens Kirche (consecracted 1309)
Main Tower
Frankfurt Höchst, including Justinus Church (church consecrated in 830)
Eschenheimer Turm (built 1428)
Goethe Turm
Chinese Garden in Bethmann Park
St. Leonhard’s Church (built 1219) Gathering point for those walking pilgrimages
Konstablerwache Farmers Market (Thur. & Sat.)
Old Sachsenhausen

for the walking tour there is Frankfurt on Foot https://frankfurt-on-foot.com/ who do both public walks and private tours. I have been very impressed.

I second Nigel’s suggestion of doing a walking tour with Frankfurt on Foot. Frankfurt has a lot to offer and a guide can enhance your understanding of what you’re seeing.