Nijmegen is a year-round city, but summer is the standout season. The Waalkade terraces open in May and the riverside is the place to be on warm evenings. July is defined by the Vierdaagse (the Four Days Marches), usually held in the third week of the month: 45,000 walkers, a week-long street festival, and an atmosphere unlike anything else in the Dutch calendar. Book accommodation months in advance if you're coming during this period — beds within an hour's drive genuinely sell out.
Spring brings tulip fields in the surrounding Betuwe region and pleasant walking temperatures. Autumn is quiet and the city reverts to its university rhythm — good for museums and cafés without crowds. Winter is cold and dark by Dutch standards, though the Christmas market on the Grote Markt is decent and the museums are uncrowded.