Wildlife SOS runs this conservation centre, which offers rehabilitation and medical care to rescued elephants. You'll get to see the elephants while touring the facility and might even be be able to help prepare their lunch. Email or phone in advance to arrange one of three daily time slots.
Volunteers are welcome here for a day or two weeks. Costs are US$100 per person per day, including accommodation and three meals at a volunteer house 10km away. Email firstname.lastname@example.org in advance.
The centre is halfway between Agra and Mathura (around 30km from both), with the turnoff near the Hindustan Institute of Management & Computer Studies.