This place was excellent! Small but cozy, with lots of light and nice touches. I loved how one full wall was basically mirrored, and the picturesque little balcony was excellent! Also, the location near the Pantheon was extraordinary and yet being tucked away meant there was no street noise whatsoever!
I also really liked the croissants and coffee made available. That helped a lot too to not have to think about running down 4 flights of stairs for coffee as I was getting ready. I could make coffee at home and get ready for my day before leaving.
It is up a very long stairwell (cool picture to take from the top) as other commenters have mentioned, so maybe not the best for less mobile persons, but it really wasn't a problem at all for me.
All in all, this was one of the best Airbnbs I've stayed at anywhere in the world due to the combination of location, amenities, and friendly service. Really just top notch!