Buses, trains and most ferry services are free on Sunday for all Aucklanders.
The super city is celebrating 100 million public transport trips in the past year.
Mayor Phil Goff says it is a great achievement for Auckland Transport.
"It makes us the third-highest city in the world to get that sort of increase in public transport over that 12-month period."
Goff is urging anyone who has never used public transport to give it a go today.
"No parking hassles, no congestion hassles. And the more people we can get on public transport, the better it is for those who are still using the road."
Goff isn't fazed by the cost - $100,000 in lost revenue.
"It's a very effective marketing technique, because if we can get people to try out public transport, once they try it they find, 'Hey - this is a good way of getting around the city,' and you're winning converts to public transport."
- Auckland Transport increases public transport fares
- $28 billion plan to fix Auckland's transport unveiled
- New Auckland transport plans the 'biggest-ever' - Goff
Hamilton is also getting on board the free public transport wave, announcing on Friday that from July 1, buses will be free for people aged 18 and under on weekends.
"Many people tell me they don't like seeing empty buses on the road," said Mayor Andrew King. "So let's full them up, let's take cars off the road, let's help the environment, let's make buses free."
And from August, the disabled community will be able to ride free anywhere in Waikato at any time.
Auckland's move follows the loosening of pet rules.