Ol'Doinyo Lengai is the "Mountain of God" for the Massai. On its top the god of the tribe has its home. This beautiful stratovolcano lies on the Rift Valley, a cliff-like scrap running from Djibouti to Mosambique. Ol'Doinyo Lengai is one of the most active volcanos of this fault - and moreover he is the only active volcano of the world with carbonatited lava.
The volcano is rarely visited, because you need two days from the next airport to reach him. Maybe one or two groups of tourists/scientists climb it a day.
The climb is not that hard - always about 45° slopes - near the top you have to use your hands because of ash and lava channels.
From Kilimanjaro Int. Airport you need about 1 hour to the town of Arusha. Take the road to the west and after 116 km you will reach Mto-Wa-Mbu (River of Mosquitos). Take the dusty road to the north (to Lake Natron, only 4x4, not during wet season) and after 6 hours you will arrive at OlDoinyo Base Camp. From there it's only half an hour to the trailhead at the slopes of Lengai.
The best way to visit the crater highlands inclusing Lengai is to organise a walking safari to the crater highlands: walk with Masai guides and donkeys through the highlands, pass Lengai and climb it!
It will take 6-9 days, you will encounter all kinds of animals and small unspoilt Masai villages.
See Kilimanjarotrips.com for prices etc. (also for Kilimanjaro trips ;-)
There are no permits required. You only need a visa for Tanzania, and there are entrace fees for the Ngorongoro Conservation Area(NCA). But if you only climb OlDoinyo you won't enter this area.
If you do the walking safari as described above you will have to pay the fees (included in organised trips).
When To Climb
You can climb the volcano the whole year round, only in the wet seasons (march to may, october to december) the roads are in bad conditions.
Be sure to bring enough water on teh way up as it's a barren and hot environment and many have become dehydrated during the ascent or descent!
Camping is allowed everywhere (only forbidden in the NCA). But think about it - the ground consists only of sand and rocks and the wind is strong. You can put up your tent on the ground of the base camp.