I've visited the 9/11 Memorial a couple of times so skipped it on this trip; One World Trade Center (ie Freedom Tower) is still jaw-dropping as the tallest building in the Western Hemisphere (the same architect designed Willis Tower and Burj Khalifa)
Church of the Covenant, an 1867 Gothic Revival masterpiece, has one of the largest collections of liturgical windows by Louis Comfort Tiffany in the country; its 236 foot steeple is the tallest in Boston
I wanted to stop at the World Famous Crochet Museum for Mike but, unfortunately, it wasn't open; the former Fotomat booth is stuffed with all sorts of crocheted pieces