The equator, the separation between the Northern and Soutern hemispheres, runs as a straight line through Western Kenya. For visitors it can be nice to stand with one foot on the Northern Hemisphere and one foot on the Southern. While elsewhere in Kenya the equator is sometimes marked by signs and curio stalls, in Western Kenya you'll have to look for it yourself. The best tool is of course a GPS, but a good map will get you close.
Of course you can't see the equator, except on a map or a GPS. However, small monuments have been erected at several places it crosses roads. One that is especially nice (and old) is in Maseno, just when you drive out of town towards the North. Great for a picture, but be careful of the traffic. Park well off the road.