This is probably Chuini palace in Zanzibar photograph taken around 1880-1890. Chuini means Leopard. The palace was built in 1872 by Sultan Barghash. This palace is located approx 10 km from stone-town Zanzibar. The building was modernised and expanded by Sultan Ali bin Said. In 1914 it was destroyed by fire.
The handwritten text on the photo says in German: Old villa of the sultan of Zanzibar (Alte Villa Sultan Sansibar)
Ref 2 also contains this photo and mentions as title Schusswani Luschtschloss des Sultans (Ref 3 Photo by J.Sturtz)