Know Before You Go
The ruins of the Muslim Walls, also known as the Arab Walls (Muralla Árabe), are located in Parque de Emir Mohamed near the Royal Palace, right across from the crypt of Almudena Cathedral.
The park is not always open to the public, but you can still see the walls from outside the wrought-iron fence. Spanish-language plaques in the park give information about the history of the site.
The closest Metro station is Opera and is connected by lines 2 and 5. The walls are located about 700 meters (about a half mile) from there. The closest bus stop is Palacio Real and you can get there by buses 3, 31, 41, 50, and 65; walk about 110 meters (360 feet) to get to the site.
As a bonus, the walls are now home to a large family of stray cats!