Apartment is well located and it is very close to Piazza Navona. And also it is close to Vatican. It is not that far from other touristic places like Spanish Steps, Pantheon and Fontana di Trevi. Be aware that there is one french bed and one sofa bed. Best way to go there from Termini is with bus No 64. Get off the bus at Tassoni stop at Corso Vittorio Emanuele. Then turn right to first street and go straight until end of the road. When you turn left you can see number 20 on Via di Panico.
It was very nice. It is very close to Duomo and central train station. The lady who works there in the morning was very nice to us. She helped us a lot. And also she knows Turkish :) Be aware that there is a bazaar everyday in front of the hostel.