To find the manmade mutant point of interest, you have to go there. You can find a human-animal hybrid inside, and also find numerous animal hybrids there.
There's even a siamese twins fetus skeleton, this secret is mostly inspired by Mary Shelly's Frankenstein.
That's also confirmed by the name this secret has in the game files.
But this easter egg is inspired by a real-life scientist as well. Before getting into that, let's look at the notes you can find here. You know the mutant is a hybrid of a bear.
A Man, a Boar, snd a Vulture. Some players think that this is a reference to south park's meanbearpig.
But that's not the case since the hybrid is also part Volture. From the last page, you know that the scientist is already tried to bring the mutant to life.
He clearly failed abandoned the experiment and never came back after that. They called the mutant immensa creatura Italian for immense creature.
The reason why this writing is in Italian.
It is because this secret is also reference to an Italian named Luigi Galvani.
Galvani was an 18th century scientist who discvered the animal electricity.
He discovered that muscles of dead frogs' legs twitched when struck by an electrical spark.
Mary Shelly herself said that Luidi Galvani was the inspiration behind Frankenstein.
This secret is may be just a tribute to Victor Frankenstein and his real-Life counterpart.