Valencia is a charming old city famous for its Fallas Festival in March, for being the birthplace of paella, for hosting the "2007 & 2010 America's Cup", and for the massive architectural project by Santiago Calatrava called The City of Arts and Sciences, an avant-garde and futuristic museum complex.
It is on the Mediterranean Sea approximately four hours to the south of Barcelona and three hours to the east of Madrid. The river Turia ran through the center of the city, but it was redirected a while back and replaced by a beautiful park. This is a very nice place to spend any free time you have in the city on a sunny day.
The city contains a dense monumental heritage (including the Llotja de la Seda (World Heritage Site since 1996) and there are several city beaches, and three major beaches outside of Valencia. Playa de Malvarrosa and Playa e Levante o de la arenas are the most popular city beaches, just north of the port. To get there, take the metro or tram to Eugenia Vines or Arenas station, or take the metro to Maritim Serreria and continue with the tram to Neptu (all on one ticket).
With only one full day to be spent in Valencia, you really ought to get yourself out of bed at a reasonable hour and head into town for some traditional Valencian breakfast. Make your way towards the Mercado Central in the heart of the city and stop in a café along the way for a couple of churros (traditional doughnut-like food) and a coffee or a large glass of blood orange juice. The town of Valencia is miraculously unpopular with tourists. Compared to most other Spanish cities, you will rarely see a tour guide leading a stampede of visitors observing the world around them through a camera lens. The only ones who make it this far away from Granada and Barcelona can typically be found in a queue outside the Oceanogràfic first thing in the morning which is exactly why the best time to go is later on in the day.
The drive to Valencia is a fairly long one and the main road is a toll road which will take you there in around 3 and a half hours. If you want to stop for lunch along the way, your best bet is to stop in Tarragona soon after you get to the coast on your way south. The majority of other towns along the route are fairly uninteresting with a score of high-rise hotels lining the shore and a distinct lack of restaurants and views. Tarragona, however, is an ancient city rich in history in culture. A decent range of restaurants in the town centre will offer plenty of choice before jumping back on the AP-7 on your way to Valencia. As you arrive in Valencia, you will notice that the city’s Old Town is strikingly different to the rest of the city that has built up around it. The city centre is confined by a river to the west and a long green park that also used to be a riverbed before the river was diverted in the fifties. As with most Spanish cities, vast numbers of affordable underground car parks are provided, so find one near your hotel and dump the car for two days as you won't be needing it for getting around.