Complex sentence: The Feathered Serpent Pyramid is located in the Ciudadela at the South end of the Avenue of the Dead, a long avenue which is surrounded by talud-tablero platforms.
Split into simpler sentences: The Feathered Serpent Pyramid is located in the Ciudadela at the South end of the Avenue of the Dead. The Avenue of the Dead is a long avenue of land which is surrounded by talud-tablero platforms.