The northernmost (and youngest) volcano in the Crater Highlands, Ol Doinyo Lengai (2878m), ‘Mountain of God’ in the Maasai language, is an almost perfect cone with steep sides rising to a small, flat-topped peak. It’s still active, last erupting in 2008. At the peak, you can see hot steam vents and growing ash cones in the north crater. Climbing the mountain is possible, but it's a serious undertaking – you'll need a guide, stamina and a head for heights.