If you could recommend only one place in the whole of America...?

Yosemite.

One of the most beautiful and famous spots in the country. There are other places of equal beauty, I think, but none as famous.

And since San Francisco is the place you get to Yosemite from, you could add that as part of your one place. Great city!

Colonial Wiliamsburg

New York City. There’s no place like it in the world. Lots to do and see.

@Cruiser Thanks for the link!

@Sunny2 Please can you be more specific. Cities are big which is why I asked for really specific areas.

Another vote for the San Francisco area. Wine country is lovely and fun, Muir Woods is fascinating with its redwood trees, Sausalito is an artsy area, it’s on the Pacific Ocean, the Golden Gate Bridge is impressive, especially during sunsets, Alcatraz prison is interesting to tour, there are trolleys, crooked Lombard Street, the ‘painted-lady’ houses, The Wharf where sea lions hang out (or used to), Chinatown, great weather, and AWESOME food. The people are friendly, and there always seems to be something going on.

Of course I’m biased toward California, but I was going to say exactly what @wundayatta said. San Francisco and Yosemite. At Yosemite, specifically the Tunnel View, which can be seen when entering on Highway 41. This is the most famous view of Yosemite and one of the most beautiful places in the world (and I’ve been all over). There are always a ton of people stopped there taking pictures. San Francisco is hard to pick one place, but I’d recommend the area near Dolores Street.

I also love Oak Street Beach here in Chicago. The beach is awesome in itself but it is right across the street from one of the best downtown areas in the world and walking distance to so much else to do. Rent a bike and ride the bike path for a great day in the big city.

The 17 Mile Drive in the Monterey/Pebble Beach area of California.

To add my own personal details to @Sunny2‘s response, Times Square in Manhattan.

Walk along Venice Beach.

If you want them to have the adventure of their lives, arrange for them to go on a police ride along in any major city.

Five Guys Burger and Fries. :/

As @SuperMouse suggests, Times square area which is close enough to walk to many museums, the U.N., Grand Central Station (Stop and have oyster Stew at the Oyster bar), the public Library (which has great exhibits). Bus to the Statue of Liberty or take a Harbor boat trip.
Broadway and the theaters, Central Park. Any kind of ethnic restaurant you can think of. Get brochures for other suggestions. It’s a never-ending fascination. And people are friendly now. (They weren’t always)

I’m also going to go with Yosemite. It is a place of natural, jaw-dropping beauty. Plus, if you like to camp, there are all sorts and degrees of camping there from Primitive, to Tent-Cabin Style.

And if you like something a lot more swanky, you can choose to stay at the famous Ahwahnee Hotel

Depending upon what time of year you go, there is a wonderful outdoor Ice Rink in Curry Village.

For convenience, there are Free Shuttle Buses which run all over Yosemite Valley, so you can keep your car parked at your campsite or hotel and see most of the sites without having to drive.

If you like Waterfalls Yosemite is the place to go.

Do you like snow and winterscapes? If so Yosemite in Winter is simply stunning.

Do you like to eat? If so, there is a lot of great food to be had in Yosemite, from fine dining to casual eateries, to snacks at the trailheads. Plus you’ll be thrilled with the abundance of Organic Sustainable Food that can be found in Yosemite.

Do you like Cooking, Winetasting or Culinary Adventures? If so, Yosemite has a wealth of cooking demonstrations, events with acclaimed chefs, and fancy culinary festivals.

Do you like to Hike, if so Yosemite has some of the best hiking trails in the world, for novices and experienced hikers alike.

Do you like Winter Activities like cross country skiing, snowshoeing, snowboarding, ice skating, sled-dogging or sleigh rides? There’s some great places in Yosemite to do all of those things during the winter months.

Feeling a bit Spiritual? Then you will love the Yosemite Valley Chapel, the oldest structure in Yosemite Valley.

Do you like photography? If so, Yosemite has some of the most breath-taking scenes you will ever experience in your whole life. It’s great for amateurs and professionals alike. Maybe you’d like to take a Photography Workshop or Photo Tour

Do you like Volunteer Opportunities? Yosemite has those too.

Read here about the History of the People and Landscape of Yosemite

Yes, I know I could be a wallking billboard for Yosemite! I love it that much : )

For me, it would have to be the Grand Canyon. It is so magnificent that it, literally, takes your breath away. Once you see it, you will NEVER forget it.

Mt. Tamalpias, Marin County, California. A drive in will get you to bird watching, an animal sanctuary, a museum, several galleries, an organic farm and bakery, a light tower, three public beaches, all kinds of small town goodies and EXCELLENT weather and coastal vistas.

Blue Spring State Park near Orlando FL. You get to see an amazing natural phenomenon (millions of gallons of water rushing up out of the Earth) plus the manatees that winter there. i have also seen alligators and other fish and birds there.

Oh man…impossibe, but yes, Yosemite is amazing. My daughter and her bf leave for Yosemite on Thurs. :-D

Disneyland.

Along the same lines as @tinyfaery, except I found Epcot Theme Park in Orlando to be a lot more interesting than Disneyland.

Any coincidence that half of these responses mention California? I think not. ;)

Washington D.C

Thanks for all the suggestions so far. I agree with everyone that says Yosemite is a must see, I was there last year and loved it. In fact, I think I texted my friend who was travelling to the States a month after we left to tell her that if she goes no where else on her trip to Cali, she must go to Yosemite!

NYC

Hands down.

@zensky Can you be more specific? Is there a particular area of New York that you believe everyone should see?

@Leanne1986 I love the city – its sights and souned and even smells. I love the architecture and history, the Village and its clubs, Soho and its galleries – the restaurants. Lincoln Center and Broadway and Off-Broadway and Off-Off-Broadway. I Love New York.