A few suggestions for sights to see in and around the Frankfurt area:
– Keltenmuseum Glauberg
https://www.keltenwelt-glauberg.de/en/
Museum about the early Celts in the region, just a stone throw away from Düdelsheim
– Büdingen
https://www.stadt-buedingen.de/
Mediaeval town with town wall, next door to Düdelsheim
– Ronneburg (south of Düdelsheim)
13th cent. castle
– Hessenpark (Taunus)
Open-air museum with historical buildings from all over Hesse and events about local culture and crafts through the centuries
– Römerkastell Saalburg (Taunus)
https://www.saalburgmuseum.de/en/
Reconstructed Roman fort with exhibitions about Roman life at the Limes frontier
– Art Exhibition „Rembrandts Amsterdam“ (Frankfurt)
https://www.staedelmuseum.de/en/rembrandts-amsterdam
Temporary exhibition of some of Rembrandt's paintings in the Städel art museum
– History Museum Frankfurt
https://www.historisches-museum-frankfurt.de/de?language=en
History of early settlements and Roman presence, of mediaeval development to the modern city of Frankfurt
– Frankfurt historic city centre
Römerberg with historical and modern buildings, St. Bartholomew's Cathedral (where emperors were crowned), Roman and mediaeval ruins
– Kloster Eberbach (west of Wiesbaden)
https://kloster-eberbach.de/en
Mediaeval cloisters with winery, film set of „The name of the rose“
and of course several „Apfelweinwirtschaften“ (Hessian Cider Pubs) in Frankfurt with traditional food!