Gather 1.5 million young people together in any small city of the world for a week. Billet them in hostels with no washing machines, bars of soap or hair dryers. Put them on a nine-mile hike the day before the last, followed by a sleepless overnight camp-out with no amenities but Porta-Potties and bottled water. Awaken them at 5 a.m. (or earlier) and have them wait four hours for a two-and-a-half-hour Sunday Mass, outdoors, under a sweltering sun. Send them back on a nine-mile return to their close quarters.

Oh, and by the way, do this in a country where less than 10 percent of them speak the local language.

Judging World Youth Day in Krakow, Poland, only from the surface, what you have is a short recipe for chaos. But that never happened during the July 25-31 event.

What else could work against WYD? When I arrived at the airport in Warsaw a week ago Monday, I had been well briefed on the logistics of what I was about to experience. After having spent the three previous days in Munich, where I had just witnessed a panicked city thrown into lockdown mode following a massacre by yet another crazed terrorist on a rampage, I could understand -- even welcome -- the ubiquitous presence of armed militia.

Because of specific warnings about ISIS, a somewhat smaller attendance than the 2.4 million originally prepared for was being anticipated. Some registrants did, in fact, pull out in recent weeks, but many others showed up who had not even registered.

Had this been a rock concert -- and there was plenty of music and celebrating to suggest comparisons -- I could not have imagined anything like what I was actually to experience. Not a single curse word, fracas or empty beer bottle thrown. No whiff of dope or signs of rowdy fans. Multinational media were all around, so one could be sure that any confrontations with authorities or hostilities between groups would have been duly recorded, if not embellished with dramatic license. But nothing of the sort has been reported - because it just didn't happen.

What broke out was peace, joy and one chorus after another of praise and "Amens." The center of attention was not the revelers or even the celebrity of the presence of Pope Francis, but Jesus Christ, who was the reason for all coming together in the first place.

The World Youth Day experience, inspired by Pope St. John Paul II more than 20 years ago, once again would work its spiritual magic, deepening the faith and passion of all those who came to seek and find a deeper relationship with the Lord, who encounters us in and through one another.

Everyone will come back with their own story, no doubt inspired by as many surprises as expectations, whether fulfilled or not. I myself had not experienced a WYD before. Our particular group of 17 joined with more than 50 pilgrims from the Archdioceses of New York and, of all places, Honolulu, through the Faith Journeys tour company, which paired these groups together.

I had decided that, if I was going to do this, I would try to spend a much time as possible with the young people. I chose to stay with them at their lodging in the Dwór Tomaszowice, a few miles northwest of the city.

While this proved challenging (I was not staying in the city with most of the bishops), I was happy to be able to share Mass, some meals and, most of all, the stories of faith and adventure that were unfolding as each one felt the presence of the Lord in different ways.

Some of what I saw was not entirely new. I had spent six years in Rome, where groups from all over the world converge throughout the year. Every group comes with their flags and songs and their own special energies. None of this was new, except that the age was much younger than the usual pilgrim populations.

Pope Francis did not hesitate to challenge the young folks attending WYD. He urged them not to give in to the mediocrity of becoming mere observers of the world, falling into false patterns of security as internet-engrossed couch potatoes.

Their role, he reminded them, was to leave an impression on the world that would change it for the better, leading it beyond the borders of national pride while respecting the uniqueness of everyone's person and heritage.

The enthusiasm for the Holy Father's presence and the love of his young "fans" was palpable. There was a certain aura of the rock star about Pope Francis throughout the gatherings, but the focus was intentionally not on him.

In the end, it was all about Jesus, the one person who formed the bond among the millions who came to Krakow. As a visual reminder of this, during the closing Mass last Sunday, the Pope's small figure was almost embraced by the image of the Divine Mercy that enveloped the wall behind the altar.

What a fitting reminder, in this Year of Mercy, that all of us have been blessed by God with the gift of His infinite mercy, poured into our hearts and meant to be shared. The bonds of love and friendship forged at this World Youth Day will, please God, open the lives of so many young people to their vocation to be, in the world, doors of mercy that will never be closed.

(Follow the Bishop at www.facebook.com/AlbanyBishopEd and on Twitter @AlbBishopEd.)