First recommendation is Las Duenas, The Duchess of Alba's home. Its a wonderful, unique, querky house with a small beautiful, cool and tranquil garden. worthy of an afternoon visit when the sun is at its highest. Allow a couple of hours, ideal from 3pm till 5pm when you need some peace and a break from the crowds as its overlooked by many. Please dont miss it!
Next up is of course the Alcazar. Its stunning and again has a massive garden with shade. We didnt book ahead but you can. If like us you want to keep your options open as to which day you go, turn up at 9am and stand in line, it soon moves along.
You will no doubt visit the cathedral. It is unbelievable, although i found it unbelievably lavish, but you should see it to make up your own mind about te history and Spanish gold from the Americas.
Be aware of The Barrio Santa Cruz and how very, very easy it is to get lost in the maze of small but curious streets behind the cathedral. Wander in for some tapas or semi authentic gift shopping, but leave the rest of the day to find your way back out!
Whatever you decide to visit while you're there, I wish you a very enjoyable time, as you can probably tell, I loved Seville when we visited last year, its a wonderful city. Interesting but relaxing, and friendly.