This is Campo San Salvador, which today seems less like a square than a transit space. In place of the tall post you see at the centre was once a well where people would tie their horses, since it was illegal to ride through the Mercerie highstreet during working hours.
The beautiful church of San Salvador is known as the most florentine church in Venice, for its elegant Renaissance façade and its cloister inside. The church famously contains two of Tiziano’s greatest works: the Annunciation and the Transfiguration.