2 Best Sights in Madrid, Spain

Built by Pedro de Ribera in 1717–30 to accommodate the Regiment of the Royal Guard, this imposing building (the facade is 750 feet long) was used as a military academy and an astronomical observatory in the 19th century. It is now a cultural and arts center with a contemporary art museum and temporary art exhibitions in some of its spaces, including the public and historical libraries. Local history professors offer free tours (in Spanish) of the building every Friday at 5 pm. In summer, concerts are held outside in the main plaza.

This triumphal arch, today a popular backdrop for photos, was built by Carlos III in 1778 to mark the site of one of the ancient city gates. You can still see numerous bullet and cannonball holes on its exterior, left intentionally as a reminder of Madrid's tumultuous past.