After leaving the Waterfront, the 19-year-old was attacked near Overdale Hospital at 1 am.
She had climbed the steps close to the bowling green on Westmount Hill and had turned right at the top towards the Crematorium when she was approached from behind by her attacker. He forced her into the field, where he sexually assaulted her.
This morning, Detective Inspector Chris Beechey declined to comment on the severity of the assault but said that the woman was traumatised and still being interviewed by specially trained officers.
Anyone with information should call 612200 or Crimestoppers anonymously on 0800 555 111.