Excellent location, nested right between Principe Real main road and Bairro Alto with a choice of the more chic bars and restaurants vs Bairro Alto's bars and Tascas. Anyone keen on a dinner with Fado will be happy to know that Cafe Luso and Foclore are both within 10 min walking distance.
We walked to Alfama and Castelo Sao George as well, no need for metros or buses (if hills aren't a deterent for you).
The flat itself has a nice little view over two gardens and a road housing some of Lisbon's pretty apartment blocks. In the evenings you can hear music from local tascas and squares giving it a great vibe. A bit noisy to sleep at night but that's the price you pay for the ideal location. Recommend staying here.