Joshua Tree National Park - Trees that impressed me. Even though I'm not a fan of cactus in general.
Everybody says - hey, the Hoover Dam - you just have to go there... na, it's the Glen Canyon Dam you have to see. An amazing bridge and dam - my friends had problems getting me away from there...
The only thing I said when I saw the Grand Canyon, was: 'This is big'.
The wooden Hotel in San Diego (where Marilyn Monroe starred in the film with Tony Curtis) is definitely as beautiful as they say.
Didn't see a lot of New York City, but what I heard was really good!
Washingon DC: in case you do not live in the center of town, try and not only walk around the White House and Capitol/ The Mall area. It took me two visits to find out that the center is around 20 minutes (by foot) away from there. Once you've found the center, you realise that there is life in DC :-)
