The Plaza de Espana is a massive semicircular structure located in the heart of Sevilla. There are several ornate footbridges that cross an artificial moat. The plaza is immediately southeast of the Universidad de Sevilla, between the Parque de Maria Luisa and the Guadalquivir River. You can get there by city bus, though it's easier to walk to all the tourist destinations throughout the center of Sevilla. The Parque de Maria Luisa is a splendid area for a picnic or afternoon stroll, although don't linger too long after dark, and always be conscious of pickpockets.
Although it can be seen in a mere 48 seconds of Episode II's runtime, you can see much more of the location in the deleted scene Extended Arrival on Naboo. It's always advisable to bring along printed screencaps from the film, though even without them, you'll find it very easy to line up the original shots. In the center of the plaza there is a rectangular structure that is flanked by two ornate footbridges. Anakin, Padme and a digital R2-D2 cross a bridge that is to the right (to the south) of the central structure. In the next shot, our heroes are walking along a curved hallway that is open to the right. This was shot to the left (to the north) of the central structure. Plan your day so that you are there in the early afternoon (around 2:30 PM) and the shadows should match up with what you see on screen.
Fortunately for filming-location hunters, there was a minimum of digital alteration, which lets you really feel like you are in Naboo as you explore the site. You will first notice that the Plaza is only a half circle, not a complete circle as shown in the film. Also, the low domed roofs that are a signature of the Naboo skylines are not actually there. Still, for ease of access and real-world Naboo aesthetic, the Plaza de Espana is a must for all location hunters!