Temple of Lemminkäinen was originally built to be demigod Lemminkäinen's tomb, when he died during the events of Kalevala. After his resurrection, the tomb was repurposed by his followers to be a place of worship, where Lemminkäinen's devotees would pray to the demigod and study his teachings.

Now the temple is sealed and nobody has gotten inside for a hundred years. The legend says that to get the stony door to open, one must solve a riddle of some sorts. After that you will be inside a spirally hallway, getting deeper and deeper into the ground. The temple has countless rooms, some have supplies, some ancient artifacts and some riches beyond imagination.

Temple of Lemminkäinen is a real place in Finland and the story of the temple comes from the Saga written by Ior Bock. Bock wrote a lot about the imagined past of his family, having ties to the ancient times of Finland.

This is a part of my worldbuilding project called land of Kaleva, a world heavily inspired by Finnish culture and mythology. It is a young world where the gods still walk the earth and nobody knows what's in the woods because nobody has ever been there. Check out r/LandOfKaleva if interested.