Terrific location in the city. Close to many great things while still being off the main thoroughfares, and a nicely updated and modernized apartment with some welcome features, including a mini-dishwasher and plenty of USB charging ports.
The stairs up are narrow and steep, as others have said. As a tall person whose feet are not small, it felt something like a ladder when going down the stairs. Use the handrail. This is probably not the right place if you have mobility issues or are hauling heavy luggage. I had only an over-the-shoulder bag and wouldn't have felt safe going up and down with large check-in size luggage. Otherwise, this is a terrific place to stay.
Not complaints, just FYI for other travelers:
All the people I interacted with in writing and in person over the reservation were great and friendly, but it could be confusing. Apart from the first automated message, I never communicated with the listed host. Instead, check-in planning and arrangements are handled by (I believe) hired agents, and I was puzzled when they began contacting me through WhatsApp instead of through the Airbnb platform, as recommended. Also, even though I replied to the first automated message with details about my transportation and arrival, I was asked for them again by someone else later through WhatsApp. Lastly, since it's Italy, you have to be checked in in person and show your passport, as hosts must register you with the local police. If your check-in agent has other travelers to meet in other locations in the city, they might not be able to meet you at the time you prefer, so plan ahead for this contingency.
Overall, I would book again: a great location, great apartment, great people, and a great visit. Thanks!