Perugia

With a population of 160,000 Perugia is not really a "hill town", it's 3 times the size of Siena and is an industrial and commercial center that's also the capital of Umbria. It's also somewhat farther away from Siena than the Tuscany Hill Towns. For these reasons, it's not comparable to the "Tuscan Hill Towns"--but is well worth a visit, especially to the old town within the walls--as long as your expectations are accurate as to the nature of the place, especially the larger town.

Very good to know! Thank you for the reply!

I went to Perugia on a trip through Umbria and Tuscany last year. I visited a number of small towns. Perugia is bigger than most Italian hill towns, but still pretty small. It's easily walked, and seems to be perched on a perfect summit to have fanstatic views in every direction. I was only there for the afternoon, but it was lovely.

I spent 5 nights in Perugia in May using it as a base for exploring Umbrian hill towns. The old town within the walls is easily explored on foot. I ventured outside the walls only to go to the bus or train station. It has a distinct university town feel with plenty of interesting art and architecture.
If you are there for dinner, there is a restaurant called "dal mi coco" that serves a great meal(two pastas, entree, vegetables, dessert and after dinner sherry) for 13 euros pp. Reservations recommended.

I have stayed there a few times using Perugia as a base for exploring the region. It's perfect for that, and a nice town in its own right. However if I understand your post correctly and you're thinking of visiting it from Sienna as part of seeing the area there are several other towns I'd visit first such as Cortona, Spello, Spoleto, Arezzo, Assisi, etc.