Auckland Council has received a submission for a below-sea-level stadium design to replace Eden Park on Auckland's waterfront.
The council's Regional Facilities Agency (RFA) has commissioned an initial study on whether a new waterfront stadium is viable to eventually replace Eden Park.
Designer Phil O'Reilly said he submitted a concept off his own back after he saw an opportunity to create something spectacular for less money.
His concept - dubbed 'The Crater' - would sit in the ocean, and a removable roof would allow people to look into it from buildings above, he said.
It would be cost-effective as there are no external architectural features to consider and politically safe as there'll be no disruption to sight-lines over the harbour, he said.
"A huge monolithic structure between the city and the harbour pretty much kills it politically," Mr O'Reilly said.
"Think outside the box - go down, instead of up."
He said the stadium would be high enough above the harbour's surface to quell concerns about rising sea-levels.
The design is a nod to Auckland's volcanic heritage and could become a landmark for the city, he said.
A spokesperson for the RFA said it was still assessing the feasibility of having a central city stadium location and was not considering any design concepts.
"If a stadium location or locations are deemed viable and the stadium project moves forward, it is possible that public or private designs may be considered or a tender process for design concepts initiated," the spokesperson said.
"But that is a long way down the track from the pre-feasibility where we are at currently."