LOCATION, LOCATION, LOCATION. The best thing about this apartment is by far its location: 2' away from the famous shop Pastéis de Belém, 4' away from Mosteiro dos Jerónimos (the Heironymite Monastery). Free parking available (5-10' walk) or a paying one right around the corner. Also, several buses and trams stops that connect directly to the centre of Lisbon (if you can get the 7 colinas with unlimited travels per day, it lasts 24h since its first use and it's only around 6€). Not far from Sintra, Cascais and Estoril if you want to visit.
Don't be alarmed by the exterior face of the building or the stairs (quite narrow and steep), the duplex is renovated and offers a quiet place with all the basic appliances to have a nice stay. However, there was a strong smell (usually at night) coming from the bathrooms, specially at night.