I haven't played CS in a few years, but recently stumbled in a video that showed the "new" (for me) Inferno map and I instantly recognized that church because I've seen it in real life. It's in Arezzo,Tuscany, Italy.
https://en.wikipedia.org/wiki/Santa_Maria_della_Pieve
Second picture shows the apse, and in the third pic you can also see that there's a fountain in front of it. Maybe they chose it because of this.