Pisac is 30km north of Cusco. It has an interesting traditional market on Sunday mornings, and less crowded ones but more commerical ones on Tuesday and Thursday mornings. You can easily catch a bus from Cusco here.
Above the town on the mountain is a superb Inca fortress. The walk up begins from the plaza, you have to ask around for the starting point. The path goes through farms and terraces.
In the central part of the ruins, known as Intihuatana group of temples, you see magnificent Inca masonry, like the Reloj Solar or the 'Hitching Post ofthe Sun', palaces of moon and stars, water channels, solstice markers.
A path leads around the hill through a tunnel to Q'Allaqasa, a military zone. cross the valley, you can observe Inca tombs in holes in the sides of the mountains.
In the enire Sacret Valley this is probably the most challenging climb. If you are planning on doing the Valley this is the place to go. If you want to take time give yourself a day for it. If you don't have that much time you can combine this with Saqsaywaman near Cusco. First do do the latter, then take a local bus (3 soles) which will take about 1,3 hours to arrive in Pisaq. From there you have approx. 1,5 hour, steep climb. You can do the whole thing in 3 hours, but I'd recommend sth. closer to 5. If you feel to tired or have run out of time, you can take quite an expensive taxi from the other side of the ruins and come back to Pisaq.