The city was yesterday inundated with red balloons tied to stormwater drains.
And if curious passersby looked down they would read a note strung to the balloon wishing people a "Happy Halloween".
Some speculated the stunt appeared to be a part of the "Red Balloon Takeover" — a global marketing campaign where red balloons are tied to drains across the globe to promote the upcoming HBO series IT: Welcome to Derry.
But the elaborate decorations were instead made by Halloween super-fan Jayne Grundy, who woke up at 5am to tie 24 balloons to drains around the city.
"I’m a big fan [of] Halloween and I just wanted people to have a surprising morning with a bit of mystery."
She had wanted to do something extravagant for a couple of years and finally got around to it yesterday, despite it being rainy, windy and dark when she was executing her plan.
The note also said "we all float down here" referencing a line from the 1986 horror novel It by American author Stephen King.
