This is a national holiday in Estonia and it is so significant that Estonians in other countries get together for it.
It's how we celebrate the shortest night of the year, which is like 6 hours and doesn't really get dark.
Minus the frog thing sadly. We don't become frogs. We just get so drunk we can't tell we're not frogs, then jump over a fire and dance around it and shit. Usually nobody dies.
Oh and then young couples go off into the forest to look for fern flowers.
OP, I invite you to come visit Estonia during this magical holiday. I won't search for fern flowers with you, but I'm sure someone will. It's not really the fun part though, the fun part is the whole atmosphere around the fire.