In addition to the typical amenities I think this means a town or city with access to great cycling roads and MTB trails with a healthy race/event schedule and cafes for recovery all within cycling or public transport distance. No car needed.
Do you know any places that fit the bill? Let’s hear about them.
I haven’t been everywhere but I think Zurich would have to been near the top of the list for places that fit that lifestyle. Grand Junction CO (Fruita specifically) is pretty amazing as well with access to some of the greatest trails I’ve ridden.
Girona
Folsom, CA
Thanks for the answers so far! I’m having a great time drooling over the pics/videos that people are posting about these places. This page on Fruita (Not in Utah) got a few chuckles from me:
https://www.utahmountainbiking.com/trails/fruita.htm
Keep those suggestions coming!
If I was a dreamer, and a lot younger, here’s where I’d go: Borg d’Oisans, France (Not sure if I spelled it right). Maybe near Borg St. Maurice, France? Val d’Isere would be nice too. You could ride up the Col d L’Iseran just for fun, either on the road or “cross country”. Or did you mean just in the US? 
We’re pretty lucky in Australia - if you ignore the car drivers.
Definitely not. The world is our oyster! I’m living in Japan at the moment.
Santa Rosa, CA Sonoma/Napa/Marin counties is a cyclist’s paradise here. All sorts of options for both road and mountain biking. I rarely need to drive my car here because everything is so close–stores, gym, restaurants, etc.
Having actuall living conditions in mind I would go from a classic cyclist point of view with central europe.
US, Scandinavia, Asia and South America: no offense. There are great places. But:
a spot where you can ride a roadbike, a mountainbike, maybe some gravel kind of stuff if you wear a big mustache, having no car so that you need a good infrastructure, some good restaurants and things like that and a variety of routes, it just can be central Europe.
Freiburg im Breisgau in Germany is a real good spot. Some WT Racers live and trains there. The town is old, nice, full of students, in the summer a lot of sun and warm. In the winter snow. You can ride from the centre of Freiburg through the Schwarzwald. A really nice forrest with a lot of hills. Or you can go there an hike, ski whatever. With a train you are in no time in the Alps with all its iconic climbs.
If you like more sea, I would vote for Nice or San Remo. Sea in front of you, hills and Alps in your backyard. Nice more posh, San Remo more long in the tooth. Really good food, a lot of sunshine, a lot of hills, good infrastructure but not many flat roads without traffic.
Someting like this.
If I just had to vote for a city for MTB I would go for Vancouver, Canada or Portland, Oregon.
Baden to the Bone(r)! So much awesome. 
You know things! 
No no. I am just googling everything that you guys are posting
But I do know enough German to get the joke though! 