Smigus Dyngus (shming-oos-ding-oos) is an unusual tradition of Easter Monday. This day (Monday after Easter Sunday) is called also in Polish "Wet Monday", in Polish: "Mokry Poniedzialek" or "Lany Poniedzialek". Easter Monday is also a holiday in Poland. It was traditionally the day when boys tried to drench girls with squirt guns or buckets of water. "Smigus" comes from the word smigac meaning swish with a cane since men tap the ankles and legs of the girls.
Dyngus comes probably from German word dingen which means to come to an agreement since the girls needed to give men money to stop being swish and splash. The more a girl is sprayed with water, the higher are her chances to get married. Usually groups of young boys are waiting for accidental passerby near the farmer markets or in the corners of the streets. Older men behave like gentlemen spraying their wives with cologne water rather than with the regular one. The girls got their chances for revenge the following day. They can spray boys with water as much as they wanted on Tuesday.
Dousing may have pagan roots, or it may reflect Christian rebirth and baptism. It may hark back to the baptism of Poland's Mieszko I and his court on Easter Monday in 966. Whether the tradition is historic or religious in origin, Smigus-Dyngus remains a significant, well-loved Polish tradition. American Polonia descendants of the 1890s-1930s immigration often celebrate Dyngus Day with a polka dance.
Let me describe two habits from my hometown Kraków that also take place during Easter season.
Emaus is a church fair (Polish "odpust") celebrated in the parish of the St. Salwador in the suburb of Kraków called Zwierzyniec. This parish was established in XII century and the fair takes place probably since the beginning of the parish. The church ceremonies of Easter Monday are accompanied with the market fair and folk festivities. Big crowds from Kraków are participating in the festivities there. The monastery of St. Norbert nuns is located near St. Salwador church and the festivities spread from St. Salwador church to the monastery.
The name of the fair "Emaus" comes from the St. Luke gospel describing the meeting of Jesus Christ with disciples on the way to Emaus that is read in this day in the churches. The wooden figurines of Jews are characteristic for this fair. The fair is enriched by the ceremonial procession of the Passion Fraternity (read more about this unusual fraternity in the article about the Lent Tradition. Also the street along the river Rudawa has been named "Emaus" after the fair.
A popular feast of Rekawka ("Sleeve") takes place on Tuesday after Easter. In the past in this day the poor residents of Krakow gathered around the Krakus Mound where rich were throwing money, food (eggs, bagels, nuts) and sweets from the top of the hill.
The Krakus Mound is one of the oldest hills with prehistoric traces being discovered. Krakus Mound is also the alleged place of burying Krakus, a first legendary prince of Kraków. Nobody knows exactly why this popular feast was called "sleeve". The historians tried to argue that the name comes from a fact that the sand for a burial place of great prince Krakus was carried in the sleeves of the residents of Kraków but it would suggest that our ancestors did not have a very clear mind unless the sleeves they were wearing were long enough so that the carrying of sand or soil could be more efficient.
I recommend a Polish customs' book written by Sophie Hodorowicz Knab, Mary Anne Knab (Illustrator). It is entitled Polish Customs, Traditions and Folklore