We stayed near Stone Town which was great for wandering around in. The market area is very busy. Watch youself in the back streets as it is very easy to get lost.
There is a huge mix of influences, so the architecture is great and you can find colonial next to a mosque next to traditional. Lots of things are Arabic influenced as it was ruled by Oman for a long time.
The museum - the House of Wonders - which is on the seafront is worth a look and then right next to it is the Old Fort which has an inner quad with local artists etc and a small cafe/bar. I bought some nice prints and photos from here. They also had live music on when we were there for the Eid break a couple of years ago.
We had a look in the Hamamani Persian Baths and I loved hanging around in the gardens on the seafront watching the world go by. We had drinks on the balcony at Africa House to watch the sun set - which a lot of people do - and also ate there a couple of times. about 8 years ago
Must visit Spice Market and Forodhoni Park in Stone Town...if you like spicy food indulge in street food at Forodhoni Park...great local grills...especially seafood. Zanzibar Serena Inn has a fabulous seafood restaurant. The hotel itself is a UNESCO heritage site. about 8 years ago
I stayed at Serena Hotel which was in Stonetown...great place plus, they have a shuttle bus that will take you to a secluded beach where you can also have lunch. Please include a visit to the slave caves which can be arranged through the hotel. We also arranged for guide to take us around the spice market and other places to shop. Walk to Mercury's which is dedicated to Freddie Mercury of Queen. The area is great as a starting point. about 8 years ago
If you make it out of Stonetown and are willing to travel around Unguja there's a lot to be seen. There is a spice farm towards the inland that takes visitors on tours. They teach you about all the different spices and allow you to taste and smell each one. It's an amazing opportunity for your taste buds to sense these things in their purest forms.
Towards the east coast you can visit Jozani National Park which is one of the only places in the world that the endangered red colobus monkey lives in the wild. In addition the park is comprised of a beautiful mangrove forest that a boardwalk runs through. about 8 years ago