You arrive at Campo San Bartolomeo while the morning light pins the Rialto statuary in sharp relief and the canals hold their breath. A private guide steps forward and the city—its alleys, bridges and quiet courtyards—begins to give up its small secrets. This two-hour walk threads through Castello, one of Venice’s least trafficked sestieri, moving from the bustle of the Rialto toward the sober stone of Palazzo Grimani, the intimate pews of Santa Maria Formosa, and the crooked stacks of the Acqua Alta bookshop where flood-prone pages lean like weathered sailors.