Need a break from the beach? Then it is time to explore the city which I also highly recommend and needs at least a full day, head to Stone Town, it is about an hour and half drive from Nungwi and Paje.
Visit the Emerson Spice Hotel which is truly gem, reserve ahead of time to have a drink or some food at their rooftop, Lukmaan is also a popular local restaurant. Check out the Darjani Market and buy their famous spices, visit the Old Fort, Foodhani gardens, Old Dispensary, Old Slave Market, House of Wonders, shop around, and explore their doors and architecture (they are very famous for their doors).
House of Wonders
The Emerson Spice Hotel
More Magic Doors