This place is amazing, the location is mind blowing, and I HIGHLY recommend that you grab it. Tomas was extremely communicative, and when I had to change the time of my arrival, he was very understanding. His uncle is the one who gave us our keys and showed us around, and he was supremely kind. He gave us tips, a little local history, and really made us feel at home. The place is a gem, and it's located in a beautiful private courtyard away from the hustle and bustle of the major streets through Santa Cruz. It felt truly exclusive, and it meant so much to be in a comfortable, quiet place - but a mere one- or two-minute walk from the cathedral and all the action.
It's a pedestrian zone, so if you have a car or have luggage, there's a learning curve I can help to lessen. You'll have to carry or roll your luggage through the narrow alleys of Santa Cruz to arrive, but it's only about 400 meters from the nearest parking garage, which we used ("Parking Cano y Cueto," which is in Google Maps). We left it there for about 36 hours, and we were charged 41 euros - so it's about 24 euros per day. You can park further away to try to save money and take a taxi into the area, but the cost of the taxi would make it all about the same - and parking seems to be expensive in all the parking garages around.
Incidentally, if you do arrive by taxi (apparently there's no Uber in Sevilla) instead of using the nearby parking garage, you can lessen the walk to the Airbnb place just slightly by asking them to take you to the "Plaza de Santa Cruz," which is within the neighborhood of Santa Cruz.
If you look at the address of the place itself in Google Maps, it looks tricky to get to, but don't worry; Tomas had us stop at the Casa de la Guitarra, which is extremely close to the place (and close to the Plaza de Santa Cruz, etc.), and his uncle showed us the place and it was all clear. In no time, you'll almost feel like you're a Santa Cruz neighborhood native!
I wish I had time to describe the magic of the Santa Cruz neighborhood itself, but I'll just say that it's worth a splurge to stay in the neighborhood. What an amazing time we had.