Kenya is a big country, the roads are not always optimal, and traffic can get quite congested. Nairobi traffic is pretty awful, and the roads leading in and out of town can get tied up with accidents, slow trucks and matatus making frequent stops. I've listed the major Kenyan tourist destinations below, their distances and the time it commonly takes to drive between them. Distance and time ratios are quite different in Africa, than in Europe or the US. Twenty miles can easily take an hour, especially as you get to the more rural roads and dirt roads inside and between parks and conservancies.
There is a good network of domestic flights, Safarlink in particular is very reliable and reasonable. It takes around 45 minutes to 1 hour to fly from Nairobi (Wilson) to Mara, Tsavo, Amboseli, Samburu and Lewa/Laikipia. And about 1.5 hrs to fly from from Nairobi (Wilson) to Malindi, Mombasa or Lamu.
But of course, flying is more expensive than driving, especially if there is more than one in your party. On the other hand, you're doing a lot of driving during a safari within the parks, reserves and conservancies just viewing the wildlife. Giving yourself a break from the bumpy roads is recommended. I find the worst thing about a safari (if there can be such a thing) is the huge amount of hours spent sitting on my bottom in a vehicle. Given the delicious food that is served at camps and lodges, this is one vacation you will no doubt be gaining weight on, despite its adventurous nature.
Distance from Nairobi to Kenya's Popular Destinations
If you prefer miles, just convert the km distance.
Nairobi to Amboseli -- a distance of 265km, takes about 4 hours
Nairobi to Lake Naivasha -- a distance of 95km takes about 1.5 hours
Nairobi to Lake Nakuru -- a distance of 170km takes about 2.5 hours
Nairobi to Samburu -- a distance of 390km takes about 6 hours
Nairobi to Masai Mara -- 250-300km (depending where in the Mara you are going to) takes about 5 hours
Nairobi to Mount Kenya/Nanyuki -- 200 km takes about 3 hours
Nairobi to Laikipia -- a distance of 290 km takes about 4.5 hours
Nairobi to Tsavo West -- a distance of 270km takes about 4 hours
Nairobi to Chyulu Hills -- a distance of 230 km takes about 4 hours
Nairobi to Mombasa -- a distance of 425 km takes about 7 hours
Nairobi to Malindi -- a distance of 575 km takes about 9 hours
Other Popular Routes in Kenya
Nanyuki/Mount Kenya to Masai Mara -- 475km takes about 7 hours
Nanyuki to Lake Nakuru -- 170km takes about 3 hours
Samburu to Lake Nakuru -- a distance of 325 takes about 6 hours
Lake Naivasha to Lake Nakuru -- a distance of 75km takes about 1 - 1.5 hr
Masai Mara to Amboseli -- a distance of 500km will take at least 10 hours (via Nairobi)
Amboseli to Mombasa -- a distance of 390km takes about 6 hours
Amboseli to Tsavo West (Kilaguni) -- a distance of 200km takes about 3 hours
Mombasa to Diani (South Coast) -- 15km will take about 45 mins (need to catch a ferry)
Mombasa to Malindi -- a distance of 120 km takes about 2 hours
Mombasa to Shimba Hills -- a distance of 40km takes about 1.5 hours (including ferry)
Mombasa to Lamu -- a distance of 320 km takes about 6-7 hours (to get to Mokowe - then you need to catch a ferry or take a private boat)
Malindi to Lamu -- a distance of 140km takes about 3 hours (to Mokowe, then catch a ferry to Lamu, see above)