My first time to Portugal! Love to meet friends! (Lisbon)

I am heading to Portugal for two weeks. Just thinking of going to Lisbon for a week from 26 dec and Porto for a few days visiting vineyard. Any recommendations on what to do during that period? I am flexible and think it is cold and just wonder what is the best for the season! I like sea, hiking, cultural stuff and visiting street market or antiques shops too!

I am from Hong Kong and first time visiting Portugal