This is a wonderful restaurant tucked away in a hidden alleyway. Okay, maybe not really that hidden as it is still in the (upper) old town of Foz do Douro area, but it is off the main streets of Praca da Liberdade, Rua dos Clerigos and Rua das Carmelitas, etc. and easily overlooked.
But it shouldn't be. This was easily the best restaurant we have dined at during our trip (June 2017; we dined here twice -- once for dinner and once for lunch). Their tapas plates are the best -- the gizzard and tripe dishes are local specialties, and the fried small sardines are most delicious and goes perfect with a glass of sangria or beer. The interior is also tastefully decorated and they seem to have a large wine selection (although we did not have a chance to try those). Their prices, especially those of the tapas plates, are quite reasonable, and the portions are pretty big for tapas.
I would put this restaurant on the top of everyone's list for dining experiences in Porto.