One of those is most definitely Pennywise the Clown, the preferred form of the titular malevolent monster in King’s gargantuan best-seller IT.
These tunnels allow Pennywise an easy way to maneuver throughout Derry, claiming unsuspecting victims all along the way.
Pennywise was of course first brought to life on-screen by genre icon Tim Curry in the 1990 miniseries adaptation of King’s novel.
As anyone familiar with the character will know, Pennywise’s primary residence is underneath Derry, in the cursed town’s gargantuan labyrinth of sewer tunnels.