A 17-year-old who admitted raping one woman and carrying out a string of sex assaults boasted about one in internet chat rooms, a court heard.
The assaults were known locally as the "Yellow Brick Road" attacks after a pathway which linked the areas where they took place.
The youth, who cannot be named for legal reasons, pleaded guilty at Manchester Crown Court to rape.
He also admitted six sexual assaults, owning a weapon and false imprisonment.
In one attack, the teenager, from Gorton, Manchester, threatened a 13-year-old girl with a broken pair of scissors in Foxley Crescent, Droylsden, before sexually assaulting her.
His last attack, on a 28-year-old woman, happened in Debdale Park when he grabbed her from behind, forced her down an embankment and raped her at knifepoint.
A DNA sample from his last victim identified the attacker as the 17-year-old youth, who worked as a health club lifeguard.
Detectives then seized his computer and found records of conversations he had had on internet chat rooms.
He had bragged about one attack on a teenage girl on several occasions and, in other chats, threatened to attack women he was talking to and made sexual threats against women generally.
Det Supt Steve Heywood, of Greater Manchester Police, said: "These were predatory sexual attacks on young women by a vicious coward, who used weapons to frighten them.
"I am pleased that he has pleaded guilty to these offences and that these women will not have to give evidence in court.
"The fact that he boasted about his cowardly and vicious behaviour and made threats against other woman over the internet illustrates what a despicable criminal he is."
He added: "I hope that he will receive a sentence befitting the nature and severity of these crimes."
The youth is due to be sentenced on 10 June.