A safari is an early-start, long-distance, dust-and-adrenaline kind of holiday. A beach is the opposite. Putting the two together in that order — never the reverse — produces the trip most people actually want, and it is why safari-and-beach routes sell as consistently as they do.
Zanzibar is the standard second half from Tanzania: white sand inside a fringing reef, dhows working the shoreline, spice farms inland and Stone Town's coral-stone alleys and difficult history a short drive from the east coast beaches. It is a little over an hour by air from the safari circuit.
Three or four nights is the right length. Fewer than three and the connecting flights consume most of the value. One practical note: the east coast has a large tidal range and the lagoon can retreat several hundred metres at low tide, while the north coast around Nungwi and Kendwa holds deeper water and swims reliably at any hour.
From Kenya the equivalent runs to the Indian Ocean coast south of Mombasa, reached overland via Tsavo East. The catalogue's Zanzibar routes are Tanzanian, but a Kenyan coastal extension can be built onto most southern-circuit itineraries on request.
From the catalogue
2 safaris in this style
Every one of these is a full route with a written day-by-day itinerary, not a template.