Miradouro de Santo Estêvão ("Saint Stephen viewpoint") is perhaps one of Alfama's least visited, least accessible and underrated viewpoints. It is located at Largo de Santo Estêvão ("Saint Stephen square"), right next to the Igreja de Santo Estêvão ("Saint Stephen church"). Like other viewpoints in this neighborhood, it overlooks Alfama and the Tagus river, but from a different angle / perspective. From here, you'll be looking to the right, not to the left as in other nearby viewpoints.
The main reason why Miradouro de Santo Estêvão is somewhat neglected by tourists and locals is because of several steep streets and stairways that make the journey quite difficult for many.
Anyhow, if you have the time and energy, it is certainly worth the visit. The view from here, though, has nothing special in comparison to the other viewpoints situated in Alfama.