The attack occurred in west Dublin at around 3am this morning.
The woman was pushing her bike towards Clondalkin village on the Lucan-Newlands Road when she was pulled into a park by at least three men.
She was then raped by at least one of the men.
The victim is a woman in her 30s, and she was taken to the Sexual Assault Treatment Unit at the Rotunda Hospital.
The scene at Ninth Lock has been sealed off and a forensic examination will take place later today.
No arrests have yet been made but Gardaí are investigating the attack.
Any taxi drivers, pedestrians, cyclists or motorists who were in the area at the time are being asked to contact Ronanstown Garda Station.
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