The main attraction at Machu Picchu is the Incan ruins.  A whole-day (or more) could easily be spent wandering through the ruins. You will want to have a guidebook that provides extensive coverage of the ruins themselves so that you will actually know what you are looking at as you hike through the area.

If you plan to spend a few days in Machu Picchu Puelbo (also known as Aguas Calientes), there are a few other sites that you can experience if you happen to get a little overwhelmed by the ruins:

Mandor Gardens & Waterfall is a 45-60-minute hike from the Machu Picchu Pueblo located off of the railway line. The hike offers an excellent trek through the forest, where you can experience Peruvian flora and fauna firsthand and see the Mandor Waterfall.  Entrance to the garden is S/10. (www.losjardinesdemandor.com)

Hot Springs -- after a long day at the ruins, you'll want to rewind at the hot springs located near to the ruins. The hot springs are located just a short walk from the main plaza. Entrance to the hot springs is S/10.

Museo de Sitio/Manuel Chavez Ballon Machu Picchu Museum & Botanical Garden -- Following the main path that the buses take, the official Machu Picchu museum is on other side the river (across the bridge).  Entrance to the museum is S/25; entrance to the botantical garden is free.

Los Jardines Botanical -- A local farmer has created a botanical garden with 400 types of orchids planted along a hillside.  The garden is in Puente Ruinas, half-way between Machu Picchu Pueblo and the Mandor Gardens & Waterfall and is about a 20-30 minute walk from Machu Picchu Pueblo.  Entrance (w/ includes a tour) is S/10.

Putucusi Mountain -- There are awesome views of Machu Picchu from this mountain. The hike takes about 3 hours and is for the physically fit.