Hi Jane
There are a few places to stay on the Delta itself. Deltebre and Sant Jaume d'Enveja the 2 main towns on the Delta are not exactly pretty places but will put you right in the centre of the Delta and will be very convenient for exploring North or South sections as the only river crossing point is between these two towns. Whether you stay in Deltebre or not it is worth a visiting the EcoMuseo there - informative displays about the formation of the Delta etc. Other towns to consider would be Poblenou or Riumar.
Just off the Delta, on the South and North and side respectively, are 2 nice seaside towns/fishing ports - Sant Carlos de la Rapita and L'Ampolla From both you can be on the Delta in literally 2 minutes.
The Delta is a rabbit warren of roads and lanes - often unsigned and for your first visit you would probably be better keeping to the main roads and the main lagoons and bird hides. A couple of years ago the Tourist Office produced a brochure with 8 birdwatching itineraries in the Terres de l'Ebre (the entire area not just the Delta) They are not always easy to get your hands on but there are 2 itineraries in there for the Ebro Delta. Assuming that you won't find a brochure in the tourist office ( I despair - don't get me on my soapbox!) you may want to download a pdf version here:
http://www.terresdelebre.org/ing/doc/birdwatching.pdf Do try to make time to get into Els Ports Natural Park and other mountain ranges around the Ebro Valley - a dramatic contrast to the flatlands of the Delta with fabulous walking trails too. If you have time there is a Vulture feeding station - big numbers of Griffon vultures often a couple of Egyptian vultures and occasionally Black Vulture. A great morning out!
As for historical sites: The Castell de la Suda and Gothic Cathedral in Tortosa. Castle in the pretty village of Miravet. Medieval villages such as Horta de Sant Joan and Batea, Escaladei monastery in Montsant (depending how far inland you want to go) Also, a little further up the Ebro Valley near where we are - lots of Civil War sites - including a museum and the ruins of Corbera d'ebre which was decimated in the war and is now a memorial village. Last but by no means least the World Heritage city of Tarragona city has some outstanding Roman remains and a Gothic quarter! How long are you coming for? !!
Be happy to try and answer any other questions. PM me if you want or email from our website or blog. (riverebro.com)
Dena