Zanzibar after a safari: the perfect place to stop.
By the end of a safari you've had a lot of early mornings and a fair bit of dust. Good news: Zanzibar is only an hour and a half away by air, and most people who add it are really glad they did.
The island has two very different halves. Stone Town is a dense, walkable, layered old port, with Portuguese, Omani, Indian and African buildings on the same street, and it's far more fun to get lost in than to follow a schedule through. The coast is what everyone pictures: white sand, dhows, and water that really is the colour it looks in the photos.
Most people give it three or four nights after a safari. Any fewer than three and the flying eats into your stay. More than five and, unless you dive or sail, you'll probably have seen it all.
The tide on the east coast goes out a really long way. On some beaches, at some times of the month, swimming is about timing, not just walking in. It's the most common surprise people have, and it's easy to plan around once someone tells you.