Seeking any and all Fall destination advice !!!

Looking to do more travelling in the Fall (September/October/November/poss December). I dont have unlimited funds, but I'm not going on a shoestring either. Would like cities with walk-ability or good ground transport factor, lots of cultural type things, and friendly folks. Not planning on partying 24/7, but would like some nightlife!
I would prefer going to destinations that arent in their high season as well... ( I have a lot of "preferences" dont I??). I will be travelling with another friend that is female, so safety is a concern as well. I know that YOU know JUST the place, so PLEASE help me out!
Thanking you in advance!!!

Lisbon, Oporto then on to Northern Spain... Santiago, Leon, Santander, etc.
Northern Spain in Autumn is really beautiful, especially Asturias and Cantabria.

Well, Germany has the Octoberfest in Sept/Oct in Munich and the Christmas markets in Dec.

Octoberfest of course is high season (biggest open air party in the whole world), most hostels in Munich are already booked solid for this time frame. An alternative to Octoberfest is Cannstadter Wasen which is held in Stuttgart at roughly the same time. You could easily explore Southern Germany after 1-3 days at Octoberfest or the C. Wasen.

Sicily can be quite nice in October I heard, same goes for Turkey and Croatia.

Well I'd say Rome, but autumn is the high season in terms of accommodation prices.