A group of us will be staying in Tuscany near San Gimignano later this year, and I'm wondering if anyone can recommend any hiking trails. For example, I see the Riserva Naturale Castelvecchio on Google maps. Any trail maps?
Too many maps. :-) We use a book called "walking and Eating in Tuscany and Umbria" by Lasdun & Davis for some itineraries though not specifically San Gimignano. Also "The Independent Walker's Guide to Italy" by Booth has a San Gim itinerary, though only 4 miles. There are tons of books. Check Amazon for options if your local store lacks depth. And always check with the locals before heading out. We've been spared some pain that way as trails tend to change.... The TI or your host can be invaluable.
Search using the acronym CAI (Club Alpino Italiano) and the word sentieri, and you'll find lots.
This link list a well known trail between Poggibonsi and San G. 'known and used by tourists of half the world' as well as the address of the local CAI office in Montevarchi.
http://www.caivaldarnosuperiore.it/tracciato_gps/toscana/anello-tra-poggibonsi-e-san-gimignano/
Another source for hiking ideas is the Via Francigena. This is the medieval pilgrim route from Rome to Spain and Canterbury, and it passes through San G. It is now pretty well marked in most parts of Italy. Have a look at this: https://www.turismo.intoscana.it/site/en/itineraries/Francigena-Leg-10-San-Gimignano-to-Monteriggioni/