The Clergios Tower looms high above the church and towers over much of Porto. It is hailed as a historical site and a place where you can get one of the best views of the city. This is a crowded attraction, so my suggestion is that you wake up and get there early. It opens at 9AM, and if you are among the first to enter, you can sail through and climb up the tower without having to worry about a crowd. The cost to get in is about $5 euro, so it is a small price to pay to see some historical church artifacts and learn about this marvelous structure. Included is a climb to the top of the tower for some great views.