Hmmm. A hard one seeing as we went with a 4 year old!
But there's go-karting fairly nearby - can't remember exactly where, but we passed it on the motorway one day.
We liked the look of Murcia. But we didn't do very much there apart from eat a traditional tapas type lunch. I think we got there a bit late and most places had closed ready for lunch. Had we got there at 9 or 10, I'm sure the shops would have been nice to have a look around.
We drove through the Valle de Ricote one day - through Archena, Ulea, Ojos, Ricote, Blanca, Cieza and others. We didn't find anything specific to get out and "do", and besides ds was enjoying a catch-up sleep, but the scenery was stunning.
A couple of the guide books and info on the web said it was a nice thing to get a boat from Santiago de la Ribera over to the Isla Perdiguera in the Mar Menor. But when we got there, we couldn't find anything, and a local bar owner said all the bars and restaurants on the island had been pulled down a year before and that the ferries didn't go any more - so you can count that one out!
We quite enjoyed walking up to the lighthouse at Cabo de Palos. We couldn't find the pedestrian entrance at first though. You can't go into the lighthouse, but it was a good viewpoint from its base, and there's a beautiful cove on one side with such crystal clear water, where there were people snorkelling. There are also some lovely seafood restaurants on the front at Cabo de Palos.