Carmen absolutely deserves a 5star as a host. Her communication and reaction time are spotless. The apartment is great, quiet and offers everything you need.
The location is perfect to visit as well the beach, the old town as the nearby Ciutat de les Arts i les Ciències. And yes, from the balcony you can see the dolphins in the Oceanografic. When participating in the Valencia Marathon this is your perfect stay as nearby to the start /finish.