Quillabamba is a city within the Southern Sierra of Peru. It is the capital of La Convención Province, which is the largest province of Cusco. It is located in an area called the higher jungle. Agriculture is the most important activity, principally coffee, cacao, tea and coca. The town is a mixture of Andean and Amazonian migrants.
Daily Buses run to Quillabamba from the Santiago terminal in Cuzco (7-8 hours, ~ 4US$) via Santa María. Turismo Ampay is the recommended company to go on this trip with. Other destinations are Ivochote (12-14 hours) and Huancacalle (4-7 hours).
Ask a taxi driver for a local guide, they can take you to see some beautiful waterfalls in the jungle. Along the way you will pass beautiful wildflowers, shade coffee trees, and oranges you can eat off the tree. There is also a small zoo about 1/2 hour away, which can be combined with a day trip to the waterfalls.
There are plenty of cheap hostels in town. Ask any cab driver.