Gutenberg Museum
A must-see in Mainz is the Gutenberg Museum which hosts one of the Gutenberg Bibles. (http://www.gutenberg-museum.de/)
Chagall Windows at St. Stephan
A visit to the church of St. Stephan lets visitors experience the very special atmosphere created by the light coming in through the blue windows created by Marc Chagall. (https://bistummainz.de/pfarrei/mainz-st-stephan/english/welcome/)
Dom zu Mainz/Mainz Cathedral
The cathedral dominates the Mainz skyline and has long been the center of town. It is surrounded by many (market) squares and the old town. (https://www.mainz-tourismus.com/en/explore-enjoy/exploring-the-history-of-mainz/churches-other-sacred-buildings/cathedral/)
Middle-Rhine Valley
The famous Middle-Rhine Valley with its numerous castles and river bends is a UNESCO world heritage site and offers spectacular views and wine hills best enjoyed on a river cruise and/or hikes. (https://www.mainz.de/freizeit-und-sport/im-gruenen/mittelrheital.php; https://www.welterbe-mittelrheintal.de/)
For a full list of things to do and sights to see, please refer to: https://www.mainz-tourismus.com/en/explore-enjoy/ or https://www.mainz.de/tourismus/index.php