Geladas live on the open grasslands at the top of the Ethiopian highlands - up to 4,400 metres above the sea. That is higher than most monkeys live anywhere in the world. The air is thin and the weather is freezing at night.
They are special in another way too. Most monkeys eat fruit, leaves and insects. Geladas eat almost only grass. They sit on the cliff-edges, pick blades of grass with their hands all day long, and chew. It is gentle, peaceful work, and they do a lot of it - up to 10 hours a day.
Gelada groups are enormous. Sometimes 600 or more geladas can be seen sitting together on one hillside - the biggest gathering of monkeys anywhere on Earth. They are friendly with each other, grooming, chatting, looking after babies. They have their own language of squeaks and grunts.
At night, the whole gelada group sleeps together on the edge of a cliff. Sleeping right next to a steep drop sounds scary, but it actually keeps them safe - leopards and hyenas can't reach them on a sheer rock face. Every morning they climb back up to start their day of grazing.