Tsukiji is most famous for its early morning fish market, but the area is still an interesting place to wonder around if you don't feel like getting up at 5 am to see the market in action.
Tsukiji is one of the biggest fish markets in the world. According to the Tsukuji Official Website they handle 2,888 tons a day of fish products. The market also caters for fruit, vegetables, flowers and meat. The fish auction starts at 5:30 am, but you can get there around 6-7 am to see the action taking place. The market is close on Sunday.

To get to the Tsukiji Fish Market, take the subway to Tsukijishijo Station on the Oedo Line or to Tsukiji Station on the Hibiya Line.
