What can we do in half day in each of these cities?

We are arriving in Nairobi in the early morning and would like to do a city tour or walk around it before taking the shuttle to Moshi. What's the best way to do this and is there any place to safely leave our luggage for a few hours?

Similarly, we have about a half day in Dar Es Salaam in the afternoon/evening on the way back. What is the best way to spend it and where can we leave our stuff?

Thanks very much for sharing your experience.

LP