The location could not get any better: top of Pena, a non-touristy area with easy* access to lively Graca, Bairro Alto, Principe Real, Alfama and Baixa districts. There's several very affordable simple local «tasca» restaurants around to try the variety of grilled meat and fish. Take a short stroll down to the Rossio train station (taking you to Sintra) or to Martim Moniz square (tram 28 starts here). The view is wonderful, the flat is small (be carefull with lintels, I've hit em with my head couple of times, but thats the only complaint) but very nice and has a style. Artur was very welcoming and gave us some proper tips.
* yes, you have to walk up & down a lot, but if you're too lazy (like we were after a night out) just take a cheap Uber or Bolt taxi, otherwise its always a nice walk