You can fly into Gibraltar and pick up a car in Spain over the border, a 2 minute walk.
Head up the coast toward Tarifa, it's a lovely drive with fantastic views over the Straits of Gibraltar over to Morocco. Head up to Tarifa for a night, lots of artisan shops and good food. Carry on then up toward Bolognia, which is the most amazing beach for swimming. Then up to Barbate, Jerez for a sherry tour and the Andalucian horses display. Take Cadiz in on the way and then Seville. On the way back take in Seville inland (very hot make sure your hotel has aircon), then Ronda which is beautiful. Not many Brits on that route and authentic. Near Ronda there's a swimming hole called Cabo de Gata - cold water to cool down in.
Depending upon how much time you have, check out some of the villages inland. Castilla for the fort, Casares, and Jimena. The local swimming pools are open in the villages and worth a swim.
There's so much more in that area. Cordoba for the Cathedral that became a Mosque then a cathedral again - and Granada for the Alhambra palace, but make sure you book well in advance.
You can also take a ferry to the African mainland. Ceuta is a Spanish enclave. Worth a trip for the fort and a lovely beach, the pool there was designed by Martianez. Beautiful and huge.
There's also a lovely museum in Tangier if you go that way. Be sure to eat at 'The Morrocan Club for lunch.
I know the area well - we used to live on our yacht in the area, it's beautiful and Spanish.