Monoliths have popped up in surprising places over the past few weeks, including an American desert, a British beach and a Belgian field.
Several of these tall, shiny pillars have now been found at sites around the globe without warning or explanation since mid-November.
The first was discovered in the US, when a helicopter crew flying over a remote part of a Utah desert counting sheep spotted a strange statue below.
This metal monolith was found on 18 November and disappeared just as mysteriously as it appeared on 27 November.
Around the same time as the Utah one vanished, a shiny metal monolith appeared on the other side of the globe in the Romanian hillside.
The structure disappeared several days after it was first spotted near the Petrodava Dacian Fortress, a local archaeological landmark in the northern Neamt country.
Shortly afterwards, a new monolith was spotted at the top of a mountain trail in southern California before it also vanished.
Then, over the first weekend in December, people stumbled across a tall shiny monolith on a beach on the Isle of Wight. The pillar was spotted on Compton Beach on the west side of the island.
A metal monolith also mysteriously appeared in the middle of a field in Baasrode in Belgium in December.
Spain, Germany and Colombia have also seen strange tall structures pop up since the first monolith was found in the US.
Back in the UK, one with the words “Not Banksy” also appeared on the top of Glastonbury Tor.
As mystery shrouded the first monoliths, an anonymous collective called The Most Famous Artist took credit for the ones in Utah and California, and is selling several replicas for $45,000 (£34,000) each.
However, when asked about the Isle of Wight structure, it said: “The monolith is out of my control at this point. Godspeed to all the aliens working hard around the globe to propagate the myth.”
A designer from West Sussex has claimed responsibility for the Isle of Wight monolith, saying he created it “just for fun”.
Explaining his choice of location, 29-year-old Tom Dunford told the BBC: “If the aliens were to come down I think they'd go for the safest place which is the Isle of Wight in Tier 1 [Covid restrictions].”
The structures have sparked comparisons with the movie 2001: A Space Odyssey, where an alien monolith is a recurring symbol that appears to play a role in the development of human evolution.
Bret Hutchings, a helicopter pilot who first spotted the Utah monolith, told local news station KSLTV he thought the structures could be from “a new wave artist” or someone who was a fan of the Stanley Kubrick film.
Speaking about the Romanian monolith, the Piatra Neamt mayor Andrei Carabelea wrote on Facebook: “There is no reason to panic for those who think there is still life in the universe.”
“My guess is that some alien, cheeky and terrible teenagers left home with their parents' UFO and started planting metal monoliths around the world,” the mayor said. “First in Utah and then at Piatra Neamt. I am honoured that they chose our city.”
Speculation has also followed the disappearance of monoliths.
A Colorado photographer told KSTU-TV that he saw four men come to the remote Utah site one night and push over the hollow, stainless steel object, saying “leave no trace” as they walked away.
Two extreme-sports athletes have claimed they were part of a group that tore down the hollow metal structure because they were worried about the damage the droves of visitors were causing to the relatively untouched spot.
Officials said the visitors flattened plants with their cars and left behind human waste.
Meanwhile, authorities in the Californian city of Atascadero said its monolith had been torn down by a group of young men that traveled five hours in the middle of the night to remove it.
“We are upset that these young men felt the need to drive five hours to come into our community and vandalise the monolith,” Heather Moreno, the local mayor, said. “The monolith was something unique and fun in an otherwise stressful time.”
Additional reporting by agencies