For a site to be given the world heritage status, it must be of outstanding universal value and meet some specific criteria. It must represent a masterpiece of human creative genius, or exhibit an important interchange of human values, or have exceptional testimony to a cultural tradition or to a civilization, or contain the most important and significant natural habitats, etc.
Here is a list of World Heritage sites of Tanzania as mentioned on the UNESCO website:
Selous Game Reserve: is certainly one of the largest faunal reserves of the world, located in the south of Tanzania.
Kilimanjaro National Park: is home to the continent’s highest mountain Mt. Kilimanjaro.
Serengeti National Park: is famous for its massive annual migration of wildebeest and zebra.
Kondoa Rock-Art Sites: the Kondoa Rock Paintings are a series of overhanging rock cliff carved into the side of a hill looking out over the field.
Ruins of Kilwa Kisiwani and Ruins of Songo Mnara: Kilwa Kisiwani – a community on an Indian Ocean island off the southern coast of Tanzania. Historically, it was the center of the Kilwa Sultanate, a medieval sultanate whose authority at its height in the 13th-15th centuries AD stretched the entire length of the Swahili Coast. It’s been designated by UNESCO as a World Heritage Site along with the nearby stonetown Songo Mnara.
Stone Town of Zanzibar: also known as Mji Mkongwe is the old part of Zanzibar City, the main city of Zanzibar, in Tanzania. Stone Town is located on the western coast of Unguja, the main island of the Zanzibar Archipelago.
Ngorongoro Conservation Area: is home to the vast, volcanic Ngorongoro Crater and “big 5” game elephant, lion, leopard, buffalo, and rhino.
The list is not in any particular order, and all these places are just phenomenal.