Where to begin? Everything feels so different there, architecture, food, climate. Practically everywhere you go there is a reminder of a history that goes back not merely scores or hundreds of years. Sometimes one may encounter artifacts or ruins that are thousands of years old. Cities also have a very different feel to them depending on whether one is in a new or old section of town. When visiting some of the small villages out in the countryside however, there is a strong feeling of things not having changed substantially in hundreds of years.
Spain has incongruities like signs prohibiting horse drawn carts on the autovias where traffic zooms by at 120+ kph. It also boasts the world's fastest train (300 kph) on the run between Madrid and Seville.
Apart from the creations of humans, the extent and variety of the natural beauty surprises and delights as well. Beautiful shorelines, tall, jagged, snow-covered mountain peaks, desert, and forests all within about a day's drive of each other. I have been to many beautiful places, and I consider those I encountered in Spain to be the equal of just about any I have encountered elsewhere. There is so much to see and experience that getting to know the area, even on a cursory level, would take months.