Yes we did, the ship is berthed in a good spot to take a walk past all the luxury yachts and up to the Cathedral etc. Takes about 45mins into the centre so allow this back.
Yes as long as your on board i think 1 hour before sailing it will tell you on display board before you go off ship remember to be back in time or you will be leftenjoy your cruise we did.
Yes you can, there are taxis outside the port building if you dont fancy the long walk in the searing heat- they are not very expensive, nice beach there too, you will pass it on way from airport to ship, next to marina- enjo.
If you can don't miss the inside of the cathedral - magnificent - & the Moorish alleyways around it, & the reclaimed land between it & the sea.