The ruins of ancient Nineveh occupy a wide tell on the east bank of the Tigris, directly opposite modern Mosul. Nineveh was the largest city in the world at its peak in the seventh century BC, capital of the Assyrian Empire under kings including Sennacherib and Ashurbanipal, and its libraries held thousands of cuneiform clay tablets — including the oldest written version of the flood myth that preceded the biblical account by more than a thousand years.
The site is accessible from the eastern side of Mosul. The reconstructed Nergal Gate, with its replica lamassu, stands at the northern end of the ruins, and you can walk portions of the ancient city walls. The inner city (Tell Kuyunjik) contains the palace mounds, and excavations have been ongoing since the 19th century. ISIS damaged several monuments here, and the Mosul Museum, which held many of the recovered objects, is reopening gradually as its collection is restored and some pieces are returned from international institutions that had them on loan.