Tate Modern occupies a converted Bankside Power Station — the Turbine Hall alone, a vast cavernous space, has hosted some of the most talked-about public art installations of the past two decades. The permanent collection spans 1900 to the present day, organised thematically rather than chronologically, which makes for some unexpected and rewarding combinations.
The collection is free; special exhibitions carry a charge and are usually worth it. Go on Friday or Saturday evening to beat the daytime crowds — the building stays open until 10pm, and the bar on the upper floors has one of the better views of the Thames at night.
The Tate Boat shuttles between Tate Modern and Tate Britain (further upriver at Millbank) — a pleasant way to split a day between modern and historical British art.
Nearest tubes: Southwark (Jubilee Line) or Blackfriars (District/Circle), both around ten minutes' walk.