In the West African country of Ivory Coast. After it was completed in 1989, the Basilica of Our Lady of Peace pushed St Peter's Basilica in Rome's Vatican City into second place.
The Basilica of Our Lady of Peace has an internal space of 30,000 square metres, almost twice the size of St Peter's, and can hold 18,000 worshippers.
However that's 40,000 fewer than the number who can fit inside St Peter's since the church's internal dimensions also include an enormous rectory and a villa.
Although it does not compare with St Peter's in finesse or beauty, the Basilica of Our Lady of Peace takes much of its design from the Vatican church.
At the front, a semi-circular arched colonnade embraces an open piazza.
The giant dome that caps the circular church rises to 158 metres, 20 metres higher than St Peter's although that measurement takes in the cross at the top of the dome, the dome itself is lower than St Peter's.
Ironically, Christians make up less than a third of the Muslim-majority Ivory Coast population.
Attendances at the basilica's daily services are usually just a few hundred.