The man, now middle-aged but who was a teenager at the time, was scheduled to stand trial in Wollongong District Court last month but pleaded guilty to two indecent assault charges on the morning the trial had been due to begin.

Neither he or his victim can be identified for legal reasons.

An agreed set of facts tendered to the court after the man's guilty plea reveal both the offender and the victim's families were involved in the running of a not-for-profit tourism attraction during the 1980s.

The court heard the man entertained the victim by giving her piggy backs around the grounds while their parents worked on the site.

On one occasion, he moved his hands from her buttocks to her underpants and began rubbing her vagina.

He also showed her his erect penis at one stage and asked her if she wanted to "play with it".

The victim repeatedly said no and the man took her back to her parents but warned her not to tell anybody what they did on the walk.

The girl told her mother what happened a few years later, but decided against reporting it to police at the time.

However, she did make a formal complaint to detectives in 2014, prompting them to launch an investigation.

As part of their inquiries, officers secretly recorded the girl, now an adult, confronting the man over the phone about what he'd done.

He admitted to his crimes, saying it had "scared the livin' daylights" out of him, that he knew what he'd done was wrong and he'd changed "the way he thought" afterwards.

"It's like when you hear bits on TV about paedos and that, I don't like it at all," he said.

"It's haunted me since the last time you called. I'm petrified this could go to the authorities or something like that."

The man will face court for sentencing in August.