The excellent company, guide & porters.
The way our porters ALWAYS found the best, uncrowded camp site.
Great food every day!
Sipping coca tea at sunrise on the last day.
The feeling of achievement as you reach the sun gate & get your first glimpse of Machu Picchu.
Quick Tips:
Whatever you do use a good, reputable company - even if it means paying a bit extra it's really worth it.
Spend several days in Cuzco to acclimatise to the altitude.
Take lots of film.
Buy your warm clothes in Cuzco rather than bringing them from home - & don't underestimate how cold it gets in the tents at night.
Best Way To Get Around:
Trekking & trains.