The Festival by H. P. Lovecraft

A man returns to the ancient, fog-shrouded New England town of his ancestors to join a secretive Yuletide observance and finds the familiar customs warped into a nightmarish ritual; led through hidden ways into a subterranean hall, he witnesses a procession of hooded figures and elder stone carvings that point to an archaic, inhuman cult and the remnants of a much older, cyclopean world beneath the town. The experience culminates in a terrifying revelation of ancestral ties to those dark rites and leaves him shaken by the sense that the present masks an older, monstrous continuity.

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