The start of the climb is from The Lewis Glacier area. The logical place to start from is from Top or Austrian Huts, which is located at 4800m. The most common way to arrive there is via the Chogoria Route.
The Chogoria Route:
You can arrive to the forest gate by rented vehicle, or by walking from Chogoria village. There are local buses to Chogoria from other major cities in the country. The forest gate where you pay the fee for the forest area, is located approx. 8km from the tarmac road. Fill your water bottles/sacks here as there is no water for the next 23 km. A walk on a bad quality dirt track takes you through dense semi-tropical rain forest. Lots of animals are heard in the bush, but you seldom see any. It is a gradual uphill which takes you from 1700m to 3050m. Just before arriving to the park gate, the dense forest disappears and rolling meadows with rough grass takes over. This area is supposed to be dangerous in the twilight hours and at night as the buffaloes and elephants come out to graze. Nice camp spot at the park gate. Taps with fresh water and a lodge nearby.
Follow the obvious track further up the mountain slopes. After approx. two hours walk you arrive at a nice camp spot next to a small river. The path gradually gets steeper and the first views of Mt Kenya and Lenana appears. Excellent camp spot at approx. 4100m at a small, but probably seasonal stream.
Mintos Hut, a rat infested hut is located at 4300m. The path is harder to find after this place, but it's not too hard to follow the cairns and green poles if the weather is fine. Some steep sections on loose scree takes you up to the eastern approahes of Lenana and circles it to Top and Austrian Hut, which is at the base of the mountain.
Heading up through the clouds
Staying in or close by Top or Austrian Hut, you're at the very foot of Lenana. It is important you aim for the left hand side of the peak or you have to walk back alternatively end up in unwanted difficulties at its much steeper south-east face.
The path is quite visible most of the time and should be easy enough to find at Top Hut. If not, walk along the path of least resistence on the snowfields below the steep rocky outcroppings. There is a rock tower visible most of the time in front of you and it's a good idea to aim at it.
Some steeper sections will appear after half an hours walk from Top Hut.
Continue in the directions of the rock tower and below the rock faces.
A rock face that is significally higher than the others will appear on your right. This is the summit of Lenana. Walk below it, not too close as rock falls are quite frequent. When you see some easy passages up to the summit ridge on you right and at the same time feel your at the highest point of the path below the peak, start looking for an easy way to access the ridge.
At a few places there are some very easy rock climbing. When at the summit ridge, walk to your right until you see a cross and some other stuff that marks the summit.
Lenana is a high mountain in tropical surroundings. Make sure to bring warm clothing as you've probably gotten spoiled by the heat and it feels colder than it actually is. Sturdy boots is a must, walking poles are great to have and wind and waterproof clothing is also essential.
Summiting the peak by the above described route doesn't require any mountaineering equipment, but if you're there during an icy period, crampons and possibly and ice will come in handy.