Three and a half hours on the appropriately named Hiram Bingham (titled for the first person to bring global publicity to Machu Picchu in 1911) will carry you from Poroy to Machu Picchu in style, with a knowledgeable guide on the way there and traditional live entertainment on the return journey.
There's an alternative train for the more budget conscious, but this one is the business if you can afford it and if you're too soft for the four-day hike along the Inca Trail. The scenery, whichever level of comfort you choose, is mind-blowing. The altitude makes the air crisp and clear.