If you visit Spain, most if not all of these landmarks are amazing to see! 
One of these is the Museo Nacional del Prado, this is one of Spain's largest Museums! Another is the Palacio Real (The Royal Palace) you can also pay to go on a tour of the palace. These beautiful landmarks are very popular too: Palacio del Crysto, Templo de Debod, and the Cathedral. If you ever go to Spain consider going to these places.

The Museo Nacional del Prado

One of the largest museums in Spain.

The Palacio Real

The royal palace located in Lisbon, Spain.

The Palacio del Cristo

The other royal palace located in the more foliated area in Spain.

The Templo de Debod

The Temple where any royalty is buried after they die.

The Cathedral

The church where people are blessed in marrage. Mostly royalty.