Cathedral of St. John the Divine to see the Keith Haring triptych. It is his last major work before his death in 1990 and depicts the life of Christ. The center panel evokes both His birth and His crucifixion. It's silver, although appeared gold in the light, and is very beautiful.
The cathedral is apparently the largest Gothic cathedral in the world. I was glad I got to see it, and I was saddened to see the damage by the massive fire in 2000 that ravaged half of it (and is now under reconstruction). However, it is clear that America's propensity for "larger" doesn't equal better. Once you've seen Notre Dame, it's hard to be impressed by American rip-offs. American cathedrals are a pastiche homage to their European counterparts.
Speaking of cathedrals, my favorite is a comparatively smaller cathedral, St. Albans in England. Obviously, cathedrals take hundreds of years to build, and times change. As a consequence, St. Albans has a nave that is partly Romanesque (with rounded arches) as well as Gothic pointed arches. It took so long to build that they switched styles to keep up with fashion. I couldn't find a great photo of it online, but I did find this old postcard where you can see the difference.