More than 1,000 participants -- a record number -- are expected to descend on the tiny heart-shaped island from Friday to Sunday, including a handful of survivors.
Breivik killed 69 people, most of them teenagers, on July 22, 2011 when he opened fire on a gathering of the Labour Party's youth wing (AUF), spreading terror as he hunted them down for an hour and 15 minutes, trapped on an island just 0.12 square kilometres (0.05 square miles) surrounded by chilly waters.
Breivik later explained that he wanted to wipe out the nascent leaders of the party, Norway's dominant political force, which he blames for the rise of multiculturalism.
Just prior to the Utoya attack, the right-wing extremist had placed a bomb near the government headquarters in Oslo, some 40 kilometres (25 miles) away, killing eight people.
"We are going to reclaim Utøya," AUF leader Eskil Pedersen vowed the day after the attacks, as normally-tranquil Norway reeled in shock from its worst peacetime atrocity.
Pedersen, who survived by fleeing aboard the only boat linking the island to shore, was insistent that Utøya remain the political forum it had been for decades.
Four years later, the site will finally reopen for the AUF summer camp in what is certain to be an emotionally-charged event.
Some families of victims were opposed to the idea that teenagers would return to the island to play football, flirt and hold fiery political debates at the site where their children were killed.
And for some survivors, it's still too soon to go back.
"I'm not sure I want to return to the camp, so I prefer to wait until I really want to go," 21-year-old Labour party member Marie Hogden told AFP.
With water up to her knees, she escaped Breivik's bullets by hiding behind a cliff.
Mani Hussaini, a 27-year-old from Syrian Kurdistan who was elected the head of AUF last year -- and who embodies the multiculturalism so reviled by Breivik -- acknowledged that this year's summer camp would be "special".
The 2012 camp was cancelled, and the two following years it was held at another location.
Families and survivors have visited Utøya on a few brief occasions.
"Those who are preparing to return to Utoya are helping to write a new page in the history of the island," Hussaini told AFP.
Another survivor, 20-year-old Astrid Willa Eide Hoem, is one of those who has decided to be there this weekend.
"It's important for AUF as an organisation and for me as a person," she said. "Utøya has to continue to be a workshop where young people learn about democracy, politics and activism."
The leafy, green island has in the meantime received a facelift. Thanks to donations and the work of hundreds of volunteers, new buildings have been built, while the old ones have been renovated with respect to the dead.
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The cafeteria, where 13 youngsters lost their lives, was initially to be torn down but has been maintained, with its bullet holes intact. But another wooden building is being built and will partially encompass the cafeteria as a
"The new Utøya should be a place to remember, to learn, and to cultivate political activism," Hussaini said.
A little further away, a memorial entitled "The Clearing" has been mounted in the woods: a giant steel ring suspended from the evergreens, bearing the names of 60 of the 69 victims.
In a sign that the wounds are far from healed, nine families did not want their loved ones' names to appear on the ring.
Breivik, meanwhile, is serving a 21-year prison sentence, which can be extended indefinitely as long as he is considered a danger to society.