Having a Sunday long walk is a nice habit, such as having a short walk after lunch. From Frankfurt, you can get with a short 20 minute drive into Taunus. Alternatively there is a frequent train connection and even a tramway, both bringing you to good starting points to begin a walk or even a hike. My favorite stopover for lunch or coffee is Anita’s Fuchstanz, a hut serving rustique but excellent food and cakes.