Ideas for you within a small radius of St Goar...
EASY HIKE #1: From ST. GOAR you will be just 5 train minutes from the town of OBERWESEL, a prominent wine town with a scenic in-town hiking trail (rated easy) that takes you along the remnants of Oberwesel's old town wall and towers. I believe we spent roughly an hour for this walk. Some resources for you:
https://www.tourenplaner-rheinland-pfalz.de/en/tour/urban-walk/oberwesel-city-wall-circuit/56218092/#dmdtab=oax-tab1
https://www.tripadvisor.com/Attraction_Review-g198501-d2189241-Reviews-City_Fortifications-Oberwesel_Rhineland_Palatinate.html
While in Oberwesel you might want to stop in at the handsome cathedral there:
https://www.weinhaus-weiler.de/wp-content/uploads/2016/08/DSC_2434_1920.jpg
EASY HIKE #2: The Günderodehaus is a top stop on this trail.
https://www.tripadvisor.com/Attraction_Review-g198501-d12125686-Reviews-Gunderodehaus_Filmhaus_HEIMAT_3-Oberwesel_Rhineland_Palatinate.html
Contact/reservations:
Günderrodehaus 1
55430 Oberwesel
Tel.: +49 (6744) 714011
E-Mail: [email protected]
I've been to the G'haus a couple times. (Never eaten there, just had a drink on the patio and enjoyed the view.) It's very close to Oberwesel - just to the south - and I walked up from town using the "Weinlehrpfad" trail at the end of town. It's a short but steep climb. I have also walked from St Goar along the Rhine Castle trail to the G-haus, but that's a tougher hike too. SO... here's a hike that I have not done from start to finish but which includes the G-Haus as well as some of the SCULPTURE PARK artwork on the Rhine Castle trail... the Heinrich Demel trail:
https://www.komoot.com/smarttour/1381648457?tour_origin=smart_tour_search
The sculptures were a huge surprise to me. Really interesting to find these things in remote spots up on those cliffs.
The good thing about this trail for you is that there's a bus from St Goar that takes you directly to the Günderodehaus on the clifftops in roughly 20 minutes. (If you already happen to be in Oberwesel, buses take you to the G-haus in 8 minutes.) Once up there, you can had out on the Heinrich Demel trail, walk as much as you like and not have to worry about the big climb from the bottom of the river gorge. You can use the DB Railway site to find bus journeys - Just use "Guenderodehaus" as your destination.
https://int.bahn.de/en/
ZUM LAMM, OBERWESEL: It was long ago but I remeember having a good traditional meal here. Didn't make reservations, don't know if you need them:
https://www.tripadvisor.com/Restaurant_Review-g198501-d7047233-Reviews-Weinstube_Zum_Lamm-Oberwesel_Rhineland_Palatinate.html
ALLA FONTANA, St Goar: Good Italian place IME.
(I have a very casual approach to eating in Germany... nothing disappoints me, so dining rec's are mostly outside my wheelhouse.)