Nancy Grunwaldt was riding a red bicycle on Tasmania's picturesque east coast in March 1993, not long after arriving in the state on holiday from Germany.
It was the last time the 26-year-old was seen alive.
Her cold case is one of eight involving women being highlighted during National Missing Persons Week.
Other cases include the 2008 disappearance of Laura Haworth, who is believed to have met with foul play after she was last seen at a friend's house in Queanbeyan, NSW.
The mother-of-two left to go to work - her vehicle was found a week later at a car park in Canberra.
Angie Fuller, meanwhile, vanished in January 2023, after running away from a car crash with her boyfriend on a highway northwest of Alice Springs.
Ms Grunwaldt and her hired mountain bike have never been found, despite searches, police appeals and a $500,000 reward for information leading to a conviction.
She died between the towns of St Helens and Bicheno, likely as a result of foul play, according to 2004 coronial findings.
Tasmania Police strongly believe foul play was involved.
"I have come to terms with the fact that I will likely never receive an answer (about) what happened," Ms Grunwaldt's sister, Frauke Grunwaldt, said on Monday.
"Nevertheless, her disappearance deeply impacted my life, behaviour and relationships over the last 30 years until today.
"It is hard to trust other people. It is difficult to open up to people.
"Thoughts of 'what if' never end. I wish I still had a big sister to talk to. Receiving an answer would finally give me closure to grieve properly."
Ms Grunwaldt was last seen on March 12 about 5km south of the town of Scamander heading south on a highway.
She was last in contact with her parents on March 11 after arriving in Tasmania from Auckland five days earlier.
About 50,000 missing persons reports are made to police every year and about 2500 people remain missing.
Australian Federal Police forensics commander Joanne Cameron said the eight cases were chosen amid conversations about combating violence against women.
She urged anyone with information, no matter how small, to call police.
"It could be the missing piece of the puzzle that brings peace to the family of a missing person," she said.
EIGHT CASES IN FOCUS DURING MISSING PERSONS WEEK
* Laura Haworth: believed to have met with foul play after last being seen at a friend's house in Queanbeyan, NSW in January 2008
* Anne Jeffery: failed to return from going to a toilet block at a campsite at Lake Arragan in NSW on August 25, 2020
* Angie Fuller: mother-of-two who went missing while travelling along a highway northwest of Alice Springs in January 2023.
* Tanya Buckland: missing since August, 2013 from rural Warwick in Queensland.
* Susan Goodwin: police suspect she was murdered and was reported missing from her home in Port Lincoln, SA in July 2002
* Nancy Grunwaldt: missing since March, 1993 in Tasmania while on holidays.
* Julie Garciacelay: believed to have met with foul play in July 1975 after being at a North Melbourne flat where an altercation involving three men occurred
* Chantelle McDougall: not seen since leaving Nannup in WA with two men in July 2007 with an apparent intention to move to Brazil
