The Carlos V is not going to impress you at all. It's and old hotel with lots of stairs (in Cusco) and run-down carpet and little amenities. The service is OK and the staff was helpful. It has a good location at 1 block from the Plaza de Armas, very centric to Cusco activities. if you like the club and pub nightlife, you're in the right street! Many bars and good eating pubs are a stone-throw distance from it. However it is not a backpacker hotel as their prices are a bit more than the value offered.
We didn't mind the hotel being old, because we spend a great deal of time out in Cusco.

Starting from the room we recived wich had a huge window without covers so there was sun from 6 am
Moving on to the fact that the hotel didnt wnat to suplly us with towels. The breakfast was so bad and discusting that we prefer to eat at resturant every morning. The stuff wasnt nice and not hapful. There is no hot water at the bathroom.After 3 night we moved to other hotel and pay less money and get much more.