Submitted by a True Travellers Society member:

http://www.intiwarayassi.org/

Inti Wara Yassi provides a unique opportunity to become intimately
involved in the care and rehabilitation of animals indigenous to the
region, including monkeys, large cats, parrots and other small jungle
creatures. The animals brought to the park generally have been
captured and sold illegally through the black market animal trade, and
have been either confiscated or given up by their owners. A minimum
stay of two weeks is required, but volunteers are encouraged to commit
to longer stays for the benefit of the animals. A small fee is
required of volunteers per month, which covers housing costs and
subsidizes the care of the animals.

There are two locations, the more commonly visited of which is the one
at Parque Machia, located in Villa Tunari between Cochabamba and Santa
Cruz (make sure you take a bus following the correct route which
passes by the park, as not all do). A newer section, Nueva Tiera, has
been opened to deal with overflow as the program expands, offering
more primitive living conditions than the original park. This is
located north of Santa Cruz.

I have personally spent 9 months at this park, and know many other
volunteers who have stayed even longer. Costs are reasonable (see the
website for details), and as long as your booze intake is minimal,
stationary life can really help in stretching out traveling expenses.
I highly recommend this experience, and suggest that one plan for a
minimum of one month stay to truly connect with the animals and
people.