The rift valley owes its existence to humongous volcanic upheaval that my mind cannot even start to imagine as we can only see the effects of this conflagration millions of years after it happened. Among the consequences that we see today are the several volcanoes that are scattered throughout its extension.
Two are close from Nairobi: Longonot and Suswa. The latter lies south of Longonot and about 50 km northwest of Nairobi. We did not visit Longonot as it implied leaving the car unattended and a long walk to the rim of the caldera. However, we did visit Suswa in several occasions as it could be reached after about two relaxed hours of a picturesque drive from Nairobi. Together with lake Magadi, it was an ideal day out although the road was rough!
The drive took us through Maasai country and there were large herds of cattle grazing on the way and around the volcano with its almost 100 km2 caldera that has a large cone towards the southern part. We saw a few giraffe, Thomson’s gazelle, zebra and hyena spoor although we never saw one.
It seems that Suswa erupted violently during the Pleistocene and this created a unique double crater with an inner crater surrounding a large block of rock. There have been more recent eruptions, perhaps one hundred years back that have expelled lava from side vents as the remaining lava flows still denuded from vegetation show.
At the time we believed that there was no water inside the caldera so we never went down and we did not see animals down despite is luring greenery.
The volcanic activity had contributed to another interesting feature: caves. These were large and they could be reached through several entrances, some easy to find and others hidden among the rocks and vegetation. While searching for the openings, great care was needed not to fall through one of the hidden holes as cows sometimes did.
There were also some rock ledges with clear signs of earlier human habitation as well as indications that these may have been used by predators, probably hyenas.
Once you entered in the caves the atmosphere became cooler and humid and some light filtered through cracks on the roof of the caves or in places where this had collapsed over time (the very same holes you and the cows needed to avoid while walking there!).
The caves had different levels of caverns and passages created by the volcanic activity and the more superficial ones are relatively easy to access if you have torches and do not suffer from claustrophobia or scared of the dark. Some were clearly enormous lava bubbles while others were like rounded tubes of rock.
We explored those caves with some natural light as our torches at that time were not up to the task of cave exploration. There was one exception when we visited the cave with Paul that had a very powerful torch that helped us to enter the darkness for a limited period as the battery had a rather short life!
During that visit we managed to enter a very large cave and walked into a large vestibule with a tall ceiling and what felt like sandy floor. The roof had rock formations with various tones of red and brown and we also saw some stalactites. The air reeked of bat pee and excrement and we soon detected the “culprits”.
Our attention was immediately called by what seemed a trembling of the walls that were no other thing that a huge number of bats hanging on. We decided to leave them alone and shone the torch on the floor and then we made another discovery!On the bat guano, tiny creatures scurried around. As I had never seen these before I collected some and, later, I identified them as pseudoscorpions, rather small tailless scorpions of 2-5 mm which were probably feeding on dead bats. There are today over one hundred species recorded from Kenya .
At some point we realized that we were sharing the air with thousands of bats and the thought of inhaling nasty pathogens spurred our departure, perhaps unjustifiably but wisely! I believe the bats were free-tailed bats of the Otomops genus, probably Harrison’s large-eared giant mastiff bat (Otomops harrisoni) only described as a new species in 2015, well after our visit. These insectivorous bats are considered vulnerable by IUCN in view of the increased disturbance to the caves they inhabit.
Several movies were filmed in Kenya at the time we were there. Apart from good ones such as “Out of Africa” there were others that left a lot to be desired. Among these was “Sheena Queen of the Jungle”, starred by the then well known Tanya Roberts, the blond of the original Charlie’s Angels.
Part of the movie was filmed in the Suswa caves and I recall that a couple of Muguga colleagues that attempted to smuggle themselves into the location of the filming to peep on Ms. Roberts, were ignominiously discovered and expelled by the security guards!
The movie, released by Columbia Pictures in 1984, is truly bad from the very start that shows Sheena galloping through an open plain on a horse painted black and white! Unfortunately, to film such a bad movie the film company left lots of debris behind showing great contempt for nature.
The movie was -justifiably in my view- nominated for the worst picture, actress, director, screenplay and musical score at the 5th. Golden Raspberry Awards in 1985 and astonishingly, it did not win any! 
As the movie required some rocks falling on the bad guys (pushed by several wild animals such as rhinos!) polystyrene rocks were left behind in the caves, together with a wooden structure where the cameras were placed.
Luckily, the Cave Exploration Group of East Africa members removed the debris that had been left behind.
 See: http://museum.wa.gov.au/catalogues-beta/pseudoscorpions
 See: https://en.wikipedia.org/wiki/5th_Golden_Raspberry_Awards