At the Convent of Christ, there are numerous busts of an old man. It's unknown who it represents; some speculate the architect or sculptor himself; others say it as allogory for the proverbial "Old Man and the Sea". Also notice the ropelike carvings indicative of the Manueline style of architecture.
As with any Portuguese city, you'll want to make sure that you note all of the interesting azulejos that you're sure to find. This one was on Rua Serpa Pinto.