The city center can be moderately to very crowded, especially during peak season (summer) and weekends. Weekdays in spring/autumn are generally less busy.
As a popular tourist destination, Delft's city center, the 'location' of `Open Delft` can experience significant pedestrian traffic. Crowds are most pronounced during the peak summer months (June-August), particularly around the Markt square and the main canals. Weekends, especially if there's a market or event, also tend to be busier. For a quieter experience, consider visiting on weekdays, particularly outside of school holidays, or during off-peak seasons like early spring (April-May, avoiding holidays) or early autumn (September-October). Early mornings are also a good time to enjoy the city with fewer people.