Country Court Judge Duncan Allen said 65-year-old Allan Richard Hodson's attack on the elderly woman in January was "spine chilling".
"It's hard to imagine any rape of this type - a rape of a stranger in a public place - that is a lot worse than that," Judge Allen said during Hodson's pre-sentence hearing today.
Prosecutor Chris Ryan said Hodson "chillingly" described to police his motivation for the attack.
Hodson told police, "Here's a good opportunity, I suppose, to have a bit of a thrill," Mr Ryan told the court.
Hodson also admitted to police his victim was frail.
Mr Ryan said Hodson, of Bairnsdale, had travelled to Melbourne that day for a psychiatric visit and had drunk four bottles of beer before the attack.
The pre-sentence hearing before Judge Allen is continuing.
The ABC reported that the judge had set a minimum term of eight years to be served.