My wife and I also like to stay several days in one place. Our first trip to Spain was this Feb-Mar. We spent 5 nights in Seville and loved it. Doing so allowed us to see most major sights as well as just wander neighborhoods which was very enjoyable. If you will be in Seville on a Saturday, spend a day in Triana where you may see spectacular weddings at local churches and beautifully dressed families gathered outside waiting to christen their children. Our Saturday doing so was a big highlight of our two week trip.
On our way to Madrid for our flight home we stayed 2 nights in Cordoba. The Mezquita is one of the most unique things I have ever seen. I think it is a not to be missed sight. We spent hours there one afternoon. Though I’m not Catholic, the next day I attended a 900am weekday Mass - it was wonderful. And be sure to climb the bell tower for awesome views of the city and countryside. There are plenty of worthwhile things to see in Cordoba. Plus along the river we found our favorite souvenirs of the entire trip in an atmospheric used book store, explored a great leather-working shop, had great meals at friendly out of the way places and clothing shopped for our newborn niece. I would have gladly stayed another day or two there.
You could easily add Cordoba as it is on the direct train line from Seville to Madrid and could be your last stop. . Or If you reversed your trip order to visit Granada last, Cordoba could be your first stop on the way to Seville. Regardless, have a great trip.
