The incident happened early on Sunday morning
Gardaí are appealing for witnesses over an alleged sexual assault in the Harold's Cross area of Dublin.
Between 5.00am and 5.30am on Sunday, the woman and a man were walking out from town through Harold's Cross onto Mount Argus Road.
At some stage along Mount Argus Road the man forced the woman against a car and sexually assaulted her.
Gardaí say he stopped when a couple approached them, and the woman walked away.
The man is described as around 6ft tall, with broad shoulders, black hair and a beard.
It is known that he was able to converse in Spanish.
Gardaí are appealing for witnesses and, in particular, the couple who saw and spoke to the man and woman, who were party standing near a car that was parked on Mount Argus Road near Laurence Court.
They are being asked to contact Sundrive garda station on 01-6666-600, the Garda Confidential Line at 1800-666-111 or any garda station.