BBC News Online's Peter Gould reports on the latest surprise move from the Pope who won't slow down.
For a man said to be in the twilight of his papacy, John Paul II still has the capacity to take the world by surprise.
Against the expectations of many, given his frailty, he led the church into the new millennium. Last month he created a record number of new cardinals. Now he is preparing for further trips abroad.
In May, he will create another piece of religious history by becoming the first leader of the Catholic Church to set foot inside a mosque.
It is being seen as an attempt by the Pope to bring Christianity and Islam closer together.
The symbolic meeting of the two faiths will take place when the Pope enters the Umayyad Mosque in the Syrian capital of Damascus.
Built in the 8th Century AD, it is the oldest stone mosque in the world, and has significance for Christians because it contains the tomb of John the Baptist.
Historic
The Vatican says it will be the first time that Muslims and Christians have prayed together in an organised way.
The Pope will lead Christian prayers, while the Muslim part of the ceremony will be conducted by the Mufti of Syria, Sheikh Ahmed Kataro.
"The dialogue between Islam and Christianity has been a difficult one," says John Wilkins, the editor of Britain's Catholic weekly The Tablet.
"There have been successes and failures, so this will be a plus for John Paul II.
"This is symbolic, like his visit to the Wailing Wall in Jerusalem, and these symbols are very important."
John Paul II has travelled all over the world since his election in 1978. He will be 81 in May, and suffers from Parkinson's disease. He has looked increasingly frail in recent months, but appears determined to continue his overseas trips.
Church diplomacy
They have enabled him to reach out to the one billion Catholics around the world. But a number of his recent visits have also had a diplomatic and political significance.
In 1999, a visit to Romania saw him become the first Pope to visit an Eastern Orthodox land since the Great Schism of 1054, which created a split in the Christian empire that resulted in centuries of mistrust and hostility.
Last year, on a pilgrimage to the Holy Land, the Pope apologised for Christianity's record of anti-Semitism by Christians through the ages. It was welcomed in Israel as part of a healing process between Christianity and the Jewish faith.
Now the Vatican is trying to improve its relations with the Muslim world. This year, a senior Vatican diplomat met Iranian government officials in Tehran. The visit to Syria will underline the Catholic Church's commitment to a better understanding with Islam.
Tensions
The editor of The Tablet, John Wilkins, believes that despite the Pope's age and infirmity, the visit to the mosque shows he has not lost his touch when it comes to making a dramatic gesture.
But there is clearly a lot of work to be done to build better relations between the two faiths.
"Traditionally, Islam has been tolerant of Christianity - more tolerant than Christianity has been of Islam," he says.
"But modern-day Islam can be very fundamentalist, and that is divisive. So on the 'holy war' side, the Pope will want it to be seen that Islam does not sanction violence."
The Vatican will be concerned about security on the visit, not least because of the tensions in the Middle East over recent clashes between Palestinians and Israeli forces.
During the Pope's visit to Israel last year, some Muslims expressed anger that he was allowed to go to the Temple Mount, close to the Al Aqsa Mosque. The divided city of Jerusalem remains a source of friction between the two faiths.
The visit to Syria shows that despite concerns about his health, the Pope has no intention of slowing down. He will return to Rome to hold a special meeting with his cardinals to discuss the direction of the church in the third millennium.
So while some commentators may talk about the final days of his papacy, John Paul II clearly feels he has unfinished business.