The Batt family went for drive up Mt Ngongotahā on Sunday.
They were left "gobsmacked" for all the wrong reasons.
"The whole lot of us were going up because the kids had not been up there for a long time, it was Father's Day and we were looking at buying a house up there," Jules Hira-Batt told the Rotorua Daily Post.
They found clothes, cans, boxes, paint pails, carpet, even the bottom of a shower, down the side of the cliff and scattered "all the way down" Mountain Rd.
"It had not just been there a day, the cardboard was disintegrating," Hira-Batt said.
"The stench, it was incredible. It is just so gross."
Hira-Batt said the family was "devastated".
"We thought are you serious? It was everywhere, consistently ... There was also significant damage to the hillside from people backing up to dump things."
She said her daughter and son, aged 11 and 12, were the most upset.
"It just did not make sense to the kids. They wanted us to clean it up and they pushed us to take pictures and put them on Facebook. 'Why don't people use bins?' they asked."
Hira-Batt said the family was "completely put off" looking for a house.