Summer (June to August) is when Rauma is at its busiest and most beautiful. The wooden town is at its photogenic best with flowers in window boxes and long northern daylight; cafes spill onto the cobbles; the harbour is alive with sailing boats. The big event is Lace Week (Pitsiviikko) in late July, with markets, exhibitions, and the famous Night of Black Lace, when locals dress in black and walk the candlelit streets after dark.
Spring and autumn are quieter. May and September are good months for walking the town without crowds, though some of the smaller museums and cafes shorten their hours. Winter is cold (well below freezing through January and February) but the old town under snow is its own reward — and the Christmas markets in December are pleasant in a low-key Finnish way.