Wappu is other name for 1st of May in Finland. Origins of Wappu are in labour unions party for labourers and after many years it has turned more and more for students' party when all towns in Finland (mostly Helsinki) are occupied with partying people.
Tradition in Helsinki is to gather at 1st of May to hill of Ullanlinna in southern tip of Helsinki cape where tens of thoudands of people are having fun and sparkling wine :)