Eminönü is Istanbul's crossroads. Located on the south side of the Golden Horn at the southern end of the Galata Bridge, it's a major transportation nexus for trains, trams and buses, and the Eminönü ferry docks are always busy.
Besides transport, it has sights: the Egyptian (Spice) Bazaar, the Yeni Cami (New Mosque), Central Post Office (Merkez Postanesi), Rüstem Pasha Mosque and Sirkeci Station.
It's a major shopping area and has been for centuries. The Byzantines bought their fruits, vegetables and grains here a millennium ago.
During the early Ottoman centuries it was the home of a Karaite Jewish colony, who were later moved up the Golden Horn to make way for the building of the Yeni Cami.
You're most likely to use the Kabatas-Zeytinburnu tram and the many ferryboats.
Eminönü has a few hotels, but there are many more in neighboring Sirkeci.
At the far (northern) end of the Galata Bridge from Eminönü is Karaköy (Galata), with its own ferry docks, tram and bus lines, and the international cruise ship dock.