About Chartres (which I really like as a - small - city), you might want to know the following... (thought I'd mention it as it comes very handy and it's not generally known by tourists/visitors!)
I've often read/heard from visitors, in particular older ones, that the walk back up the lower town (basse-ville) to the upper town is a bit of a PITA, esp. for people with mobility problems (such as my wife), as it's steep, whether you take the 3 or 4 tertres (staircases linking the 2 levels as it were) or just walk up to the upper town on the pavement.
For over ten years now, there's been a small and free HOHO shuttle (no ticket/card needed) that will take you back up to the upper town, they call it locally the "Navette Filibus" (navette = shuttle and Filibus being the name of the local transportation authority, http://www.filibus.fr/. This is the map of the whole transport network for Chartres & suburbs:
http://www.filibus.fr/ftp/FR_document/web-Chartres%20SCHEMATIQUE%202022%20210x210%20mm%20(2).pdf
The new (electric) shuttle looks like this:
https://www.chartres.fr/fileadmin/user_upload/actualite/2021/filibus-c-la-navette-chartres-metropole.jpg
Its official name is "Relais des Portes", as the shuttle goes from "porte" to "porte" in the old town (in the upper town too, goes to the railway station, to the start of the pedestrian area on Place des Épars, it has a stop close to the cathedral etc.), so it takes in the ancient gateways to the medieval town (those gateways were destroyed during WWII, only Porte Guillaume has vestiges. You might know that Porte Guillaume area of Chartres for its beautiful half-timbered houses and lovely mews, bridges etc. There's a few locally famous restaurants too. L'Estocade for instance, it has a terrace on the banks of the River Eure. So does the superb riverside Moulin de Ponceau, next door practically - that one's posher though but has a good-value three-course menu for €33 https://www.restaurant-moulin-ponceau.fr/).
There are plans to rebuild the Porte Guillaume identically, but it's been in the offing since 2015 and not much has happened since then (Chartres Métropole isn't massive in terms of population, only about 120,000, but has had an ambitious mayor for over a decade and invests massively, meaning that secondary/non urgent projects have had to take a back seat - major recent investments include the Odyssey swimming & aquatic complex - Europe's largest apparently - and Chartres en Lumières. and as a result the municipality of Chartres is a little broke,m although they derive quite a lot of € from the many big companies that have settled within the intercommunalité limits, particularly well-known ones internationally are the cosmetics & perfume ones, Guerlain & co, they have a big R&D unit there... Chartres is at the heart of the so-called Cosmetic Valley, there's an international cosmetic centre in Chartres etc.
You can see what Porte Guillaume looked like in medieval times here: http://www.lesportesdutemps.com/archives/2020/02/03/37996707.html
Anyway, this HOHO shuttle stops at the various "portes" and in other places too in the upper town. They added two new routes last year. It's dead handy!
Every 20 minutes, from 6.40 am to 23.30 (every day except Sundays and bank holidays).
This is its route: http://www.filibus.fr/ftp/FR_document/RELAIS%20DES%20PORTES.pdf