Great place to watch the sunset in Rome. The drawback is that it can get a bit crowded with all the tourists and people hawking their wares. There is an elevator from the Spagna metro stop to the top for those that might have issues climbing all the stairs. It is worth climbing up for some decent panoramas of the city.
It's amazing how the churches that appear small in Rome look so grand inside, while churches that look grand like the Trinità dei Monti can actually be so modest within. This church, located at the top of the Spanish Steps, holds regular service that visitors can participate in. It's also full of art, though not as much as many of the other churches in Centro Storico.