The interresting things in Porto are all within walking distance. This way you can enjoy the beautifull views from every high point you walk past.
And if you are tired you can always catch a taxi. All taxis in Porto have the same beige color. And are found on many streetcorners or squares.
As usual, like every where Taxi drivers will try to be funny with excuse like airport surcharge and waiting surcharge etc to charge you more. Whether it is Europe or India- everywhere it is same. They are trying to earn bucks but be frank to ask questions and dont shell out extra money for anything or find nearest policeman to report harassment.