Google on cooperation with the US National Park Service offers 360 degrees through Street View for 40 National Parks and Cultural Monuments of the United States.
In addition to his virtual tours Street View, you will have access online museums exhibiting historical objects and national treasures with full description and accompanying history brochures.
Perhaps in the near future vacations will take place behind a screen and a headset. However for now because the plane ticket to the US is quite high, the said virtual tour it is the most economical solution to see the country's national parks. Virtual vacations are just two or three mouse clicks away.