Being greeted by Princess, an African elephant, feels like being checked out by the nozzle of an industrial vacuum cleaner. With her small eyes focused keenly on mine, she suctions my chest, then my legs, and makes a beeline for my hair. She's a yard from me and there's no fence. As she deftly takes out my hair grip, her minder Dirk says, "Just let her go at her pace, let her come to you. Don't do anything sudden." The end of her trunk is ridiculously agile, like a pair of human fingers. I realise the greeting is coming to an end when she lifts up her trunk and high fives me.
"I'm fascinated by how elephants and humans interact," says Dirk. "We don't ever ride the elephants; just communicating with them is an electric experience."
Some people and animals are worth travelling great distances to meet. Princess, Dirk, Carlos Da Silva and his horses are among this select group. "We sell space," says Carlos. "Emotional, physical and geographical space." In fact the Chua Cho Farasi (School for Horses) offers horse treks, hiking, kayaking, mountain biking and elephant whispering – all set in a private game reserve in Tanzania, in the shadow of Kilimanjaro. And, unlike many high-end local safari options here, the people at Chua Cho Farasi are able and willing to adapt to your budget.
A fully catered tented camp in the bush, complete with flushing toilet is one option. A basic bedroom in an outhouse is another.
For the hardcore, there is cooking over an open fire, with a bedroll in a tent. There is also a scheme to offer accommodation for long-term stays on the farm, where you help out, or do your own research. Be warned, though: living conditions are basic. There's solar power only between 9am and 6pm, and luxuries such as the internet are strictly limited – but it's a very cheap, and unique, experience.
I stayed at Casablanca, Carlos's farmhouse, which has two small outbuildings with single beds, mosquito nets and a table in them. With the oil-lamp flickering and the croak of frogs outside, it was an atmospheric place to spend a couple of nights.
Ndarakwai lodge, a couple of miles up the road, is distinctly posher. The tents on offer here are mini houses, complete with carpets, bedspreads and armchairs. With Carlos your food is a hearty goulash of half cabbages, potatoes and chunks of lamb. In Ndarakwai you can expect silver cutlery, bone china and delicate salads.
What's most impressive about a stay here are the riding safaris, and for good reason. The level of horsemanship and guiding competence required here is exceptionally high. It's a dangerous landscape out there: the animals are wild and the terrain is rough; it's easy for a horse to stumble and break its leg. "It takes me about 15 minutes to work out the client's level of riding by watching them on horseback, and we discuss what they might enjoy," says Carlos.
Carlos watches me guide his seven-year-old one-time race horse through a river, at a walk. I've been riding since I was four, competent enough, apparently, to later manage a brisk gallop following zebra. There is something exhilarating – and mildly terrifying – about riding at dusk. This is the golden hour, when lions, buffalos and elephants come to the watering holes. As we ride along, I realise that my horse and the wildlife are checking each other out. Horses have much better hearing than us: they stop and listen; flared nostrils tell you there are animals nearby. Compared with travelling in a vehicle, it's an intimate, graceful form of transport.
Horses also love running with zebras and gazelles; it is hard to resist the thrill of keeping up with a herd of these beautiful creatures. Then, as the light fades, we come across a freshly killed zebra, still with its flesh and hide intact. Carlos becomes very serious. "There are lions or cheetahs around. Let's move. Are you OK to gallop for a bit?"
Carlos was once an elite Spanish horseman, then went to work for Greenpeace International (he was captured on film dangling by his ankles in chains to protest against Japanese whaling in the Mediterranean). These days he lives a quieter life, two hours from the nearest small shop, along a spine-jangling dirt road, on a game reserve lodged between Mount Meru and Mount Kilimanjaro in Northern Tanzania. On one side is the Selous game reserve, on the other the Serengeti.
His staff consists of four young men with troubled histories. For five years they've worked together, learning to shoe, groom and care for horses, as well as gaining safari-guiding skills. Ronaldo was once a child miner near the Congolese border. At 16 he left the mine and came to Arusha where he lived on the streets until he joined the Watoto Foundation, a Dutch charity that works with street children. With a glowing reference, he was later given a placement with Carlos.
After a three-and-a-half hour ride in the morning, and a two-hour ride in the afternoon, I'm more than a little saddle-sore, but I've seen more game than on many a week-long vehicle or walking safari. This is how riding should be: animals everywhere, stripped of pretension and pomp, a sense that East Africa is far more regal and ancient than a tourist brochure can ever convey.
* Chuo Cha Farasi ( ecotourism-africa.com/farasisafari.html) offers a range of riding options, from equestrian horse clinics for advanced riders to day-long rides in the Kilimanjaro Conservancy.
* Carlos Da Silva's farm, Casablanca, is part of the Kilimanjaro Conservancy, and within a private game reserve of Ndarakwai, which is 100km north west of Arusha, in an area called West Kili. If you want to book a place as a long-term volunteer or a shorter stay including safari horse riding, contact Carlos (00 255 784 994 181; firstname.lastname@example.org). He is happy to host long-term volunteers, particularly those with skills in solar power, water management, carpentry, plumbing, building, web design, marketing, agriculture and gardening, equestrianism, zoology and biology.
* Alternatively, stay at the permanent luxury tented lodge, Ndarakwai (00 255 27 250 2713; ndarakwai.com), where doubles start at $297 (£200), full board.