Take Tram 28 for a great ride and it stops right in front of the Cathedral.
This is the oldest church in Lisbon, with construction on the church commencing in 1145. At the end of the 13th Century, the cloisters were built later in the location of the previous gardens. King Dinish of Portugal ordered the cloister to built in Gothic style. They were damaged in various earthquakes that hit Lisbon, but significantly damaged, as was the Cathedral, with the 1755 earthquake.
On our visit in 2016 there was an archeological dig underway in the centre courtyard of the cloisters. The dig has been going one for a number of years and they are finding Roman and Visigothic remains as well as part of the former mosque wall.
There is a small fee to enter the cloisters, well worth it. The cloisters themselves have three 14th century tombs.
The cathedral is dark, but I found the cross-vaulted galleries very dark and they are in need of a cleaning (2016) - in many areas the walls were actually black. But, nevertheless the cloisers very impressive.