Tuonela is the realm of the dead or the underworld in Finnish mythology. It is yet to be proven to the public that this construction is not another Entrance to Tuonela.
Some claim that, potentially to prepare construction of Vermonniitty, an utility tunnel was built under Perkkaa and this would have resulted in the need for beautiful constructions like this providing access to it. But those lack imagination
Kindly put the cache back exactly as it was, it will only hold in a very limited area.