Here is a list of ideas:

1-In Germany for the summer solstice we celebrate the Wasserearden, where we explore by boat the lakes of Germany. In particular, the tradition is alive in the state of Mecklenburg, known as "the land of a hundred lakes".
2- In Finland the summer solstice is Juhannus, the central focus of the celebration is the kokko, the bonfire that drives away evil spirits. You dance around the fire and you also hope to find love. According to a popular legend if a maiden puts seven flowers under the pillow before falling asleep, in a dream she will see the man to be married.
3-In England, the summer solstice is celebrated in Stonehenge, Wiltshire. The Druids considered it a spiritual center and an astronomical observatory.
4-In Spain the summer solstice corresponds to the feast in honor of Saint John. Large bonfires are lit, bursting with old furniture and books. It is a gesture of purification that provides for a new beginning.
5- In Belarus and Ukraine the longest night of the year is called Kupala Night. They organize parties, bonfires to dance at night. Women entrust their hopes to lighted candles floating on the rivers. While men bathe at midnight to purify themselves.
6-In Macedonia there is one of the oldest astronomical observatories in the world, that of Kokino. Here people gather to observe celestial phenomena during the summer solstice.
7- In Italy, to attract good luck, it is necessary to spread out on the dew during the night of San Giovanni. In Benevento there is a walnut tree under which it is said that once the witches gathered for a sabbath: the inhabitants must protect themselves with rosemary and blessed olive tree on the doorstep. In the countryside fires are lit to keep away the spirits, while in Florence on the roofs of the basilicas were placed pots full of fat for a fire fed all night and visible from afar.