In reply to Camerontaylor158:
Public transport-wise Switzerland and Austria are good. Zillertal you will struggle but Magic Wood (CH) and Silvapark (A) would be great. Magic Wood has more of a climbing scene, Silvapark is quieter. It depends what you're looking for. Magic Wood is amazing for higher grades, less good for Lowe grades. Silvapark has poorer landings, very sharp rock if your skin isn't in condition and would be ok in September but by October might be out of season. Not sure about pad hire in Silvapark. Both Magic Wood and Silvapark have a decent campsite options - either a short bus / skilift away or directly at the boulders. Both world class venues.
Someone mentioned Albarracín. Tbh you could get there by public transport, Airbnb in the town and hitch to the bouldering easily. It's a five minute ride and there would be people heading that way all the time. Pad hire at the climbing shop, very skin friendly and tonnes of amazing climbing in lower grades, stable weather..
Fontainebleau gets a mention. Without a car it can be done, but probably involves wild camping and that's frowned upon really.
There are tonnes of other places but those fit your criteria pretty well. Wherever you go you'll be back, for sure.
Worth being flexible though. You can easily get a week of rain in the Alps and in Font. Albarracín less so.. Wales might be a good back up..