I lived half a year in the second city of Portugal for my Erasmus. Here is a little list of nice things to see and do in Porto.
Big and beautiful azulejos in the entry of the station showing the history of Portugal (consisting in a lot of battle with Spain).
My favourite place for breakfast, no tourist and good food.
Scenic view of the city.
Beautiful market building with restaurant inside.
Nice gardens with a great view over the city/bridge arrabida.
City with beach - has many restaurant with fresh fish from the harbour. Easy access thanks to metro.
Traditional market, very Portuguese, you can eat in the center.
In Vila Nova de Gaia, once you have crossed Luis I bridge, go down and visit one of the winery: Ferreira (the only remaining Portuguese - the rest are British), Taylor, Sandeman, Calem… to understand the different types of porto and how they are made in the Doro Valley (Golden valley).
Famous night life street, full of bars.
Contemporary Art Museum designed by Álvaro Siza Vieira, a famous Portuguese architect. It’s a bit outside the city, but it has a nice park and a villa to visit as well.
Bonus : Enjoy a very cheap beer in the student bar Espaço 77 🍻