The Olympic flame will have an unusual home for the Rio de Janeiro Games.
The flame will burn somewhere in central Rio during the Games, and not in a stadium as has been traditional at the summer Olympics.
Rio spokesman Mario Andrada said the cauldron will be lit at the Maracana Stadium during the opening ceremony on August 5 and "go from the Maracana to downtown. But exactly where remains a secret".
Unlike recent Olympics, Rio will have two stadiums: the Maracana for the opening and closing ceremonies and football, and the Olympic Stadium across town, which will be used for track and field.
Mr Andrada said "we had our share of thoughts before coming to this".
"It's impossible to have two cauldrons, and it's impossible to have the same cauldron in two places," Mr Andrada said.
Central Rio is not typically visited by tourists, who usually flock to the Copacabana and Ipanema beaches in the southern part of the city.
The city centre is also remote from the Olympic Park in the western suburb of Barra da Tijuca.
The mystery surrounding the cauldron is one of several regarding the flame, which arrives in the capital Brasilia on May 3.
The flame will be lit at a traditional ceremony in Greece on Thursday.
Some of the confusion centres on Brazilian president Dilma Rousseff, who will skip Thursday's ceremony in Ancient Olympia.
Brazil will be represented in Greece by sports minister Ricardo Leyser, and Marcelo Pedroso, the head of the Olympic Public Authority.
Ms Rousseff is fighting impeachment and could be suspended from office in the next few weeks if the Brazilian senate votes to hear the charges against her.
Plans call for Carlos Nuzman, the head of the Rio organising committee, to get off the plane early on May 3 and be greeted at the airport by celebrating athletes.
The flame then goes to the Planalto presidential palace. Even if Ms Rousseff is still in office, it is unclear if she will light the first torch for the three-month torch relay around the country of 200 million.
A spokesman for the president's office said that the plans for the ceremony were not set.
If Ms Rousseff is suspended by May 3, vice president Michel Temer would take over, putting him in the Olympic picture. He would also be set to preside over the opening ceremony with Ms Rousseff sidelined.
International Olympic Committee president Thomas Bach and local organisers hope the flame's arrival will generate enthusiasm for South America's first Games, which have been touched by political corruption scandals, a deep recession and the Zika virus.
Organisers have also trimmed about $500 m in spending on the Games, cutting 20,000 volunteers, food services and transportation. Ticket sales have also been slow and a few venues are behind schedule.