Dordrecht is most pleasant from late April to early October, when the canal-side terraces are open and the boat trips into the Biesbosch run on a regular schedule. The main festival of the year is Dordt in Stoom — held over a weekend at the end of May in odd-numbered years — which brings around 200 historic steam-powered boats, trains and machines to the harbours. It is the biggest steam event in Europe and turns the whole old town into a moving museum.
Other times worth aiming for: the Jazz in Stoom festival in June, the November film festival if you read Dutch, and the Christmas markets along the Voorstraathaven in mid-December. Winter is grey and quiet but the cafes are cosy and museum-going is rewarding.