It's a wonderful (hilly) walking city with fabulous views, food and drink and really friendly, safe feeling. Take comfortable shoes and pick up/take a brolly.
Walk across the top of the Dom Luís bridge and soak up the beautiful view - sunrise or sunset best! Explore Gaia's waterfront, take the Ramos Pinto port tour and enjoy a few port cocktails along the front looking at pretty Porto lights twinkling. For the best Francesinha, walk up the hill to Bufete Fase for opening time (there will be a queue forming) quite quickly - it's all the day, go hungry and enjoy a beer with it! We also tried Cafe Santiago, which was fun experience, very buzzy, but Bufete tasted best!
Enjoy nata from Manteigaria and dust with cinnamon as they taste so much nicer!
Take the tram on the circular town ride and down to the beach - I loved that it was a mix of us tourists and locals using it. We walked everywhere other than that as so many interesting side starts streets and beautiful, faded tiled buildings to gaze at - didn't have a duff coffee or meal anywhere!
Livraria Lello is beautiful but it was packed! You can buy a ticket in the shop further up the corner you skip the queue and offset it against a purchase. If you love bookshops (I do) it's worth it! There's a beautiful shop nearby, A Vida Portuguesa, with the loveliest gifts etc - the soaps are gorgeous smelling and make wonderful gifts (Claus Porto £££ or Ach Brito £) and just along that street is a great bar, Galeria de Paris. I loved it - service was relaxed but hey, you're on holiday, I loved the decor and one evening there was a cabaret act on with wonderful jazz piano. There was also an arts & crafts street market on that street on the Saturday.
The delis and bakeries on R.Formosa are stunning to look at and explore eg
A Pérola do Bolhão I just wanted to try everything!
Hope you have a wonderful time - we loved it!