Ngong Hills is really beautiful and easy to access from Nairobi. The entry was 600 KES for tourists and 200 for nationals. We're told it is not safe to walk all seven hills alone as theft/mugging has increased on the route. We walked four on our own and had no issue as there were plenty of people around. You can pay for a ranger which is likely worth it with a group if you want to do all the hills. If you want a break from the city and some fresh air this is a great place to go.