The best time to visit Sandomierz is late spring (May–June) or early autumn (September–October). Summer brings warm weather and long days but also the busiest crowds, particularly on weekends when day-trippers arrive from Kraków and Warsaw. The Old Town is small enough that even modest crowds can feel significant.
Autumn is particularly good if you want to visit the vineyards — harvest season runs from late September through October, and several of the local wineries host events and open their tasting rooms. The loess hills turn golden and the views across the Vistula valley are at their best.
Winter is cold and often grey, but Sandomierz out of season has a stillness that suits its character. Christmas markets are held on the market square in December.