This is the BEST location in the city. I am so glad I stayed here with the beautiful traditional neighborhood instead of Bairro Alto or Chiado -- they were lovely to visit, but not to stay in.
I would use the host's instructions to check in, because that is the easiest way to find the apartment in the first place. However, from then on I would recommend Ubering places from the Museu de Fado. it's downhill from the apartment with no stairs, and it will be easy for cars to find you.
Please know this apartment is small. It was tight for my parents and I, but it worked. I'm 24 and I had no problem with the ladder to the beds, but it wasn't as easy for my parents.
This was the perfect choice for our trip!