A grey-brick shikumen lane house in Xintiandi where, between 23 and 31 July 1921, thirteen Chinese delegates and two Comintern representatives met in secret to found the Chinese Communist Party. A French Concession police raid on the eighth day forced them to finish the meeting on a boat at South Lake near Jiaxing.
The room has been preserved (with later furnishings) and an attached museum tells the history of the founding and its participants. The CCP treats the site as the equivalent of an apostolic origin point, and on key anniversaries the queue can run round the block. At normal times you can walk straight in. Free entry but you need to book ahead online.