We had a wonderful time staying at Carmen and Iris's place. Our hosts were super helpful and provided us with information about current events and activities in Valencia (e.g., the Christmas markets).
The location very close to the Estación del Norte (main railway station of Valencia) and Calle Colón is excellent. The old town and several major metro lines with direct connection to the airport are within easy walking distance.
The flat is clean and very well equipped - the kitchen makes it easy to self-cater. The décor is modern and very nice. The flat is on the 4th floor of a building with a concièrge and can be accessed by a lift. The ground floor can be accessed from street level not only by stairs, but also by a ramp. The flat is very quiet, which allows visitors to rest after a busy day in the city.
Overall: highly recommended!