Located in Belem, this tower is an UNESCO world heritage site. The tower was built in the 16th century. You’ll have to pay to get there so if you already went to the Discoverers monument, I’d leave this one out if you’re not that into the thing. Views from the other monument are better. However, every site, except for discoverer’s monument, is free to access on Sundays so if you’re in Lisbon for a few days, save Sunday for Belem.