With its amazing colors, vintage cars, great food and colonial architecture, Cuba is high on my list of places to go. Right now american citizens cannot enter into the country without a special reason such as research, visiting a relative, or filming a movie. However, travel restrictions are slowly but surely changing. The US consulate recently re-opened in Cuba and there is a lot of talk that american commercial flights will soon start servicing the country.
That said, the opening up of tourism for americans into Cuba will likely drive up prices and reshape the country's preserved culture. For now, if you want to get to Cuba, you can enter by taking a flight from Canada or any other country that flies there. I know americans who have done this with no problem, even thought it isn't technically legal.