Three weeks in one place

Just an idea: If you also want to make use of highspeed trains then Brussels is I think a location to consider.
Some rough figures: Paris 1½ hour, London 2 hours, Koln 1¾ hour, Amsterdam 2 hours and with the local train Bruges 1 hour.

Mechelen and Leuven (or think even about Ghent) are nice little towns close to Brussels, add a half hour to get to railwaystation Brussels-Midi where the highspeedtrains stop. The mentioned towns have also easy acces to the freeways for making daytrips with the car. You can also think about B&B´s somewhere on the countryside, I think enough options for staying somewhere.

In September weather can be fine, but there will be likely stormy weather too. To be more sure about good wheather you have to look more closer to the Mediterranian area.

Hi,

In that case, other than the UK, I suggest Vienna, Paris, or Berlin. Ordinarily, Paris would fit the bill just fine. Berlin is for more esoteric sites you may want to visit within a 2 hr radius or so by ICE train. Vienna with slower trains to outlying areas and sites.

Reading your post and about the rest of your trip being more hectic sightseeing I think somewhere in either Provence or Tuscany would be a bit more relaxing and day trips around either are easy with a car. A smaller city with a good selection of restaurants and a nice area for evening walks would be ideal. If you're outdoorsy types, somewhere in Bavaria or Austria would be nice too.

The Options are endless. Here is an answer to a similar request: https://community.ricksteves.com/travel-forum/general-europe/1-months-travel

I could very much enjoy, and do at least once a year, setting up one or two base camps from which I do day trips and / or overnight trips. Because of my bias one of those camps is always Budapest but there are an infinite number of places to choose from.

I agree, the options are endless. So, choose based on what's convenient for the rest of your itinerary, or based on what place interests you. For instance, staying in Tuscany is a great plan - if you want to see Tuscany and Umbria.

Since want to drive for this portion of your trip, I'd want to stay in a place that was not so easy to see, or see all of, by public transportation. Some that come to mind immediately are some areas of France (Dordogne - especially cave paintings - and villages in Provence) and Italy (Umbria, southern mainland provinces like Basilicata, Sicily). As a non-driver, these are the places I wish were easier to see without a car.

Just to give one specific recommendation, if you want to have a base in Sicily for a few weeks, I would highly recommend the agriturismo I stayed in near the center of the island: https://community.ricksteves.com/travel-forum/italy-reviews/sicily-caltanisetta-central-sicily-agrigurismo

Or, if you want a more urban Sicilian base (and don't mind being in eastern rather than central Sicily), this house would be perfect: https://community.ricksteves.com/travel-forum/italy-reviews/siracusa-airbnb-in-ortigia

While neither of these places is geared for a long-term rental, with the kind of advance notice you have, you should be able to stay there for a few weeks.

If you need ideas, in addition to reading travel books, you can watch videos. Rick's are on Hulu, or on YouTube via his website: http://www.ricksteves.com/watch-read-listen/video/tv-show

Your general plan is a good one.

This being said, it is hard to give a tip without you giving us a clue, at least, of what kind of environment and/or activities you are interested in. Do you want a location by the ocean? Somewhere more mountainous?

As others said, possibilities are really endless.

Personally, I'd use those 3 weeks to visit and explore, without any rush, areas that are often not easy to fit in an "on-the-go" itinerary, such as Sicily or Calabria (Italy), Sogn of Fjordane (Norway), central Pyrenees (Spain).

You could also consider one of the islands of the Azores, Madeira or Canaries, summer holiday crowds will be mostly gone by mid-September and you can explore your island in a slow pace (car being always very helpful).

All these places I mentioned are good locations for these "fixed base for 3 weeks + car" arrangements. If you are interested, you should find plenty of info on websites for each area. Just beware of over-relying on tips (including the ones on RS books) that are often meant for fast-paced visits only. Explore the online resources and find what you like and which place could entice you to stay put for these 3 weeks.

You shouldn't have trouble finding holiday rentals in any of them at that time. I'd start my trip with this 3-week sojourn before going on the fast-paced part of the itinerary, because big cities are less affected by the occasional drab Fall strom weather system and shorter days.

We go to Europe for extended periods of 6 - 9 weeks at a time and usually plant ourselves in one place for a minimum of 3-4 weeks to get to know different areas fairly well and experience a little bit of what life is like!
Here are some of the places we have stayed and really enjoyed.
* Paris - we stayed in a suburb called Gif sur Yvette to make it easier to drive to sights outside the city. It's a quiet town right on the RER line. Some days we rode public transport into the city and others we drove the car and parked it in a garage in Passy.
* The south of France in Languedoc - we stayed in Pezenas, a beautiful, lively little town. Easy to get to many interesting places in southwest France...beach, vineyards & wineries, the Cevennes, lots of hilltop villages, many historic sites, etc. The town of Pezenas has a great weekly market and the many winding streets make it great to explore and just wander looking for a place to have dinner.
* Switzerland in Valais near the Italian border - best of both worlds! Hiking and walking in the mountains, gorgeous vineyards and wineries, fresh fruit in abundance, castles, picturesque villages, and accessibility to Italy if you have a hankering for delicious food and wine!
* Other places we have enjoyed staying for long periods are Rome, Amsterdam, Belgium, and in the Hessen region of Germany.
So much to choose from! Good luck and let us know where you end up!

The north coast of Spain comes to mind, as do smaller countries like Slovenia or Denmark, which have a lot to see within a drivable distance.

Great suggestions! Thanks very much, everyone.