Caving -- Besides its wildlife and scenic attractions, the Chyulus shelter Leviathan, believed to be the world's longest lava tube, a geographic phenomenon formed by hot lava flowing under a crust that has already cooled. Here, at some point on the hillside, part of the surface crust collapsed, allowing air to enter and causing a tube to be excavated just beneath the surface -- the resultant hollow is a fascinating draw for anyone looking for a serious caving adventure. In global terms, lava tubes are relatively rare; they form only under specific conditions with lava of a specific type and viscosity. Savage Wilderness Safaris (tel. 020/712-1590;, one of Kenya's top adventure activity operators, runs 3- to 4-day trekking and caving expeditions, which include time spent exploring sections of Leviathan; besides typical cave phenomena such as stalactites and stalagmites, you see elements associated with volcanic activity, such as lava ropes and sinkholes. It's not just about geology, though. You'll also walk the crest of the hills, taking in phenomenal views of the plains below and, weather permitting, glimpsing mighty Kili in the background -- it's just 50km (31 miles) away. Encounters with any of the Big Five are a distinct possibility; plains game will often be spotted. Tents and sleeping mats are provided, as is all food and cooking equipment. Porters, however, are not provided, so you'll be responsible for carrying your own equipment (including a share of food and tentage), meaning you'll want to travel ultralight.

Africa's Green Hills on Horseback -- African safaris are popular and also big business. There's every danger in some spots of discovering yourself caught up among a cluster of frantically reversing Land Cruisers while the predator you're supposedly tracking has long since legged it back into the bush, far from curious humans. The Chyulu Hills are among the best places in Kenya to visit for a complete escape from the crowds. This is a true wilderness, with almost none of the development seen in the country's most popular parks and reserves. And the landscape is particularly unspoiled. The Chyulus are also where some of Kenya's prime horse-riding safaris are conducted. If you stay at Ol Donyo Wuas, you'll have ample opportunity to explore the region on horseback and at night return to some of the most comfortable quarters imaginable. Award-winning U.K.-based travel outfit Black Tomato (tel. 207/426-9888; arranges smart, all-inclusive saddle-safaris guided by experts who will take you cantering with large herds and hopefully put you on the trail on some of the more elusive predators -- it's not uncommon to spot cheetah while out riding. At night, in contrast with the sturdy walls and leather-and-wood luxury of Ol Donyo Wuas, you'll bed down in canvas in a luxury mobile tented camp with all the trimmings. Each trip is tailor-made, so costs, duration, and routing will depend largely on your interests.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.