The Santa Justa lift is one of top attractions in the city. You really can't miss the lift since it peaks out from all the buildings in Lisbon. It will give you the bird's eye view of the city.
I wasn't interested in paying money to use the lift so we ended up walking up the hill and somehow, found a back entrance. No one was guarding the back entrance for some reason. We saw a couple of people walking in so we followed and quickly took photos. You only have to pay to go up the lift and also you need tickets to go to the top observatory deck. I'm not sure why we somehow got access but I was happy to take a couple of panoramic shots for free.