Hamilton has racked up $255.89 million in new debt in the past five years - with Claudelands Event Centre tagged as the single largest contributor.
New figures show the event centre and city roading contributed to half the council's new debt since 2007.
The city council proposes to cut services and sell assets to pay it off.
Next month the city's total debt is expected to reach $400 million - and more than half of this was due to recent spending.
In response to the figures, the council's finance and monitoring committee chairman Dave Macpherson said hindsight showed the council made some wrong decisions.