Although not cathedrals in the European sense, when in California, we enjoyed stopping at the Crystal Cathedral near Annaheim. Very modern, but spectacular with lovely grounds. We also enjoyed several of the missions along the coast, in particular San Diego and Santa Barbara.

I concur with Notre Dame in Montreal and St. Anne deBeauprey in Quebec. If you go to the latter, be sure to visit the beautiful chapel on the lower level - spectacular mosaics.

Chicago:

If in Chicago - I'd encourage a visit to Old St. Pat's. (Downtown -- 700 West Adams) One of the oldest churches in the nation (1846) and one of the few buildings to survive the great fire of 1871.

Irish Catholic and really beautiful. It is airy, light and bright. Nothing like the old churches which remind you of death and damnation....

If you are lucky enough to be in town for 11:15 Sunday mass given by Fr. Cusick, you would be in for a real treat -- all are welcome.

I think the National Cathederal in Washington, D.C. is stunning architecturally. It's less beautiul inside, but the grounds are also beautiful. For new church architecture, the new Los Angeles cathedral is also quite interesting.

If Montreal counts as the U.S., then I would add the Oaxaca Cathederal and the Santo Domingo church in Mexico.

If you are ever in Cincinnati be sure to go across the river to Covington, KY. I believe it is called the Cathedral of the Basilicia of the Assumption. My friend and I were visiting Cincinnati for a weekend and drove over to Covington to attend mass there. Even though neither of us are Catholic, we enjoyed the service and were awed by the beauty of the cathedral.

Just 1.5 hour south of chicago is the Notre Dame Cathedral in South Bend, IN. As a Hoosier who grew up in South Bend I have always found it to be one of the most beautiful churches that I have ever seen, anywhere!

I see no one has mentioned my two favorites.

The Basilica of the National Shrine of the Immaculate Conception is in D.C. and is the largest Catholic church in the country. There are many different areas to explore inside the church, it is well curated, and of course, the architecture is stunning. It is on the grounds of Catholic University of America.

The history of the Mary, Queen of the Universe Shrine in Orlando, Florida, is intriguing. It is basically the church that Disney tourists built. A priest started ministering to tourists in 1975, his vision grew, and since then, it has been growing in leaps and bounds, funded almost entirely by tourists. The grounds now hold a lovely sanctuary, an outdoor chapel, a museum, gardens, fountains, objets d'art, and the ubiquitous gift shop. An audiovisual center all about the history of Catholicism is the next project. I have been attending services when in the area since my parents brought me as a child, and there is a special inspiring spirituality that always comes through. (I'm not even Catholic anymore, LOL).

Hope you visit many peaceful places of worship!

Oops, sorry. I see now that someone did mention the Basilica previously. Sorry about that.

St. Nicholas Church in Pittsburgh. Enjoy the art of Maxo Vanka.

http://www.post-gazette.com/ae/20010...ls0927fnp2.asp

http://www.stnicholasns.org/

St. Mark's in Seattle is not a very interesting building, but if you're there on a Sunday evening and want to experience a wonderful service to put you in the right frame of mind for the coming week, they have a fabulous choir which sings the monastic service called Compline. I believe it begins at 9:00 p.m. and lasts about 35 minutes. It was started years ago, and many, many (hundreds) of college & HS students attend for the serenity & beauty that it brings to life.

Calvary Episcopal Church in Pittsburg is a lovely space. Christ Church in Grosse Pointe Farms (outside of Detroit) is nice, with a fine choir. Chicago has Holy Name Roman Catholic Cathedral or St. Luke's, Evanston. Unity Church in Oak Park is an interesting example of Frank Lloyd Wright architecture.

Happy travels.

In Pittsburgh, at the University of Pittsburgh: http://www.umc.pitt.edu/tour/tour-090.html

This is the chapel that is a part of the Cathedral of Learning, which, although not a place of religious worship, is an interesting building nonetheless.

On a little different tac.....I believe some of the oldest churches in the U.S. can be found in the southwest. Try the San Xavier del Bac Mission, just south of Tucson if you're ever in the area.

Thank you everyone for contributing these great suggestions. Appreciate those that responded for the cities I listed above.

But also hope that others will continue to add their recommendations. It's fascinating to hear about places all over North America.

Thanks to those that have suggested attending services as well. What a welcoming idea!

I second the recommendation of Detroit church tours. St. Anne's is the second oldest Roman Catholic parish in the US. As I recall, the oldest one is in Florida.

Don't think this was mentioned yet --

Charleston, SC has some lovely (smaller) cathedrals complete with excellent music programs to showcase their accoustics. I think its also referred to as a "Holy City" because of its numerous churches.

The visitor center had a comprehensive brochure / guide that also had an insert with current musical listings.

I, too, love churches and castles. Someone mentioned the Basilica in Covington, KY. Gorgeous. And across the river in Cincinnati on top of Mt. Adams is the gorgeous Holy Cross Cathedral.
http://www.hciparish.org/
But the National Shrine in D.C. is still my favorite! Love the doewnstairs. BTW, they serve a great breakfast there.

This may not be EXACTLY what you're looking for, but I've always been attracted to people who have felt led to create religious art work. They are invariably far from hustle and bustle, allowing quiet contemplation. The Ava Maria Grotto in Alabama is my personal favorite.

Duke Chapel, on the campus of Duke University, Durham, NC

http://www.chapel.duke.edu/home/

Beautiful setting, esp. in spring when there are flowers blooming all around the place.

If you happen to be in San Jose, CA, St Joseph's Cathedral is really beautiful.

http://www.stjosephcathedral.org/history.asp

yet another vote for Grace Cathedral in San Francisco. I liked walking the labrynth, which is a copy of the one in the Chartes Cathedral.

The Shrine of the Most Blessed Sacrament was built in a field in Hanceville, Alabama (near Cullman) because of a vision by Mother Angelica. It's a beautiful sight to behold. Master craftsmen from Italy and Germany contributed to this remarkable church. For an online tour http://www.olamshrine.com/olam/shrine_guide.htm