Both towns are situated on high hills, offering great views of the surrounding countryside. It's worth trekking all the way up to the castle ruins in Assisi to have a long look in every direction.
Quick Tips: Both towns are worth checking out thoroughly, but there is no need to stay overnight, especially if you see one per day like I did. Make an early start in the morning and you'll see it all and return to your base camp in Florence before the sun sets.
Best Way To Get Around: It's not easy getting up to the top of the hillside towns, so grab a bus from the Assisi train station, and in Orvieto catch the funicular ride up the mountain.