There is a lot to do in Portofino if you are ready to take in a completely different type of an experience. First, exploring the Italian Riviera never gets old. The Marina Bay here is so beautiful that you can spend hours gazing deep into the sea. To explore more, you can take ferry rides from here and also go for yachting tours. Swimming and fishing is also permitted although quite a bit of caution is advised.
Apart from this, walking around the city exploring its churches and simple yet enriching history is one of the best things to do while in Portofino. You should visit all the three churches and explore the different history that has gone into making them.
You should also try out the authentic pizzas, pastas, gelato as well as various other Italian delicacies such as the tiramisu, risotto and ravioli at the cafes here, your stomach and tongue will thank you forever. Another thing to do here is to visit the Castello Brown which is located at a slight hike and is one of the best places to get a panoramic view of the city.
Although, not exactly frequented by tourists you can also walk down a little from the hill and access the beautiful lighthouse of Portofino. Around this area, you will also find a conserved national park looking area which has a variety of flora and fauna for you to explore on your walking track. If you want to go to the beach, then just go to the road that connects Portofino to Saint Martin and there are a lots of beaches on this particular stretch.
If you feel the city is too small for you and you have a lot of days, then exploring the Ligurian coast is not a bad idea either. You can take the ferry and get to any of the places located nearby on the Riviera to get a completely fulfilling experience. Alternatively, you can also go explore the artistic side of Portofino by visiting its famous gallery and analyzing the beautiful paintings housed inside the churches here.