Sé de Lisboa, or simply Sé, is also known as the Lisbon Cathedral or Catedral de Santa Maria Maior ("Cathedral of Saint Mary Major"). This is the oldest church in the city, built in 1147, right after Lisbon was conquered by Christians against the Moors. The construction took place in the precise location of the medieval mosque. It survived multiple earthquakes (mainly the one that happened in 1755) and represents several architectural styles. 

If you are walking through Alfama, it's simply impossible not to notice or pass by this majestic construction. It is located very close to Igreja de Santo António ("Saint Anthony church") and Miradouro de Santa Luzia ("Saint Luzia viewpoint"), Miradouro das Portas do Sol ("Portas do Sol viewpoint"), Castelo de São Jorge ("Saint George's Castle") and Teatro Romano de Lisboa ("Lisbon's Roman Theater").

Make sure you use comfortable footwear while walking through the steep streets of Alfama! A nice way to get here is by tuk tuk too.