Tharapithia is a Great Old One as well as being a Slavic and Ugric God-like creature. Known as the Shadow in the Crimson Light, it is a photophobic and burrowing fiend awed in the Middle Ages. It cannot endure sunlight, and eludes it by tunneling deep underneath the roots of oak trees.
An encounter with this horrendous deity is detailed here, taken from a journal that was thought to have been lost during the end of the Medieval Period:
"...in the Arabian chronicles it was mentioned as the Forest of the Thousandfold where the fierce being of the pagan worship reigned: the Slavic and Ugric godlike creature Tharapithia, who could not endure the light of the sun eluding it by tunnelling deep under the roots of the oaks. Old tales spoke of the German raiders cutting down a small portion of the forest down by the seaside, as for revenge to the natives, who had looted and destroyed the newly built chapels, which were in their mind too close to the groves that they held sacred. The old tales do not explain the way the armour-clad and blessed warriors were slain and ripped to pieces by something that had no natural position in the perpetum mobile we call Life. But they do tell that the entity was not pleased with the roots of the mighty oaks drying up and dying, so It could no longer suck on them for nourishment."