COLOGNE — In liturgical events culminating the XX World Youth Day celebrations in Cologne, Germany, Pope Benedict XVI called on the youth to become missionaries in a world that is forgetting God, and highlighted that only a “true revolution” which comes from God can transform the world.

The climax of World Youth Day took place in two back to back celebrations at Marienfeld — an abandoned mine 17 miles from the center of Cologne whose grounds were prepared to welcome around one million young pilgrims from around the globe.

For many traveling to World Youth Day with the Archdiocese of Boston, sharing their faith with Pope Benedict XVI and fellow Catholics from around the world were the highlights of their pilgrimage to Cologne, Germany.

The pope arrived in Cologne on Aug. 18, travelling the Rhine River by boat and addressing pilgrims before he paid homage to the cathedral and drove through the streets in his pope mobile. Hundreds of thousands of pilgrims lined the river, crowded around the cathedral or gathered along the streets to catch a glimpse of the new pontiff.

“It was really cool,” Jackie Poremski, 19, said of her first time seeing any pope. She and the rest of her group from Blessed Kateri Tekakwitha Parish in Plymouth listened to Pope Benedict speak to the crowd gathered along the riverbank.

“I like him. I think he’s a worthy successor,” she said. “He’s not afraid to say what he feels even though it’s not always popular.”

Kate Hanley, 20, from St. Christine Parish in Marshfield attended WYD in Toronto three years ago and said it was strange at first to see a new pope. Her group also heard Pope Benedict speak, and she said he did not “talk down” to the adolescents who came to listen.

“He was speaking to us,” she said.

Daniel Horan, 27, waited to take a picture of the pope when he drove through the streets of Cologne. The crowd was shoulder to shoulder and grew very excited as the pope mobile came by, said Horan, who traveled with the Archdiocese of Boston but works with young adult ministry in the Diocese of Manchester, New Hampshire. They chanted “Benedetto,” both while waiting for him to arrive and as he approached.

“It’s almost like being near a rock star,” he said.

Almost 500 pilgrims from Boston, 158 with the official archdiocesan group, arrived in Germany on Aug. 15 and most flew home on Aug. 22. Half of the main group stayed in Cologne while the other half was in nearby Düsseldorf. Due to the number of participants, accommodations could not be made for the whole group in Cologne, and other pilgrims from Boston were scattered throughout the area.

Throughout the week pilgrims endured many hardships in order to participate in WYD events. They commented that they were at times tired and hungry, squeezed onto overcrowded transportation and often had to wait in long lines. The week for many was physically draining as well as spiritually invigorating.

Boston pilgrims were reassured by the large number of participants.

“It’s wonderful to be in a large community or gathering that’s so different from the secular world where initially people are stand-offish or outright hostile,” said Horan. “In this gathering of almost one million people it’s hard to find someone who’s not friendly.”

Brother Jason Zink, BH, a campus minister at Boston University, said he hoped pilgrims would experience the fullness of the Church at WYD and find new friends who would allow them to “see our commonality in Christ.” Once that happens, the students hopefully develop a greater love and openness for others, he said.

“The world gets smaller after these events,” he added.

Jackie Dion, 17, said she found that the experience of WYD affirmed her faith.

“It’s just so good to know there are so many Catholics out there and so many people who want to see the pope,” said Dion, from St. Joseph Parish in Medway.

Pope Benedict also met with almost 5,000 seminarians attending the WYD celebrations, Aug. 25. Carlos Suarez, who is entering his first year at St. John Seminary in Brighton next month, said meeting with so many of his fellow seminarians was encouraging.

Suarez said he was seated about 20 feet from the stage where the pope spoke about what it means to live a priestly life, a life of sacrifice and giving of self. The pope’s words were “strengthening,” he said.

Those who traveled from the Archdiocese of Boston had the opportunity to meet with Archbishop Seán P. O’Malley and share their favorite WYD experiences with him on Aug. 19 at their hotel in Cologne.

One woman from Blessed Kateri Parish said she met a man who had been praying for the intercession of their parish’s patron saint for a couple who was trying to adopt two Native American children. Members of the parish spoke with him and gave him a pin from their church, and he said that he saw their meeting as a sign that his prayers would be answered, the woman added.

A young pilgrim shared her enjoyment of attending Mass with many people who spoke different languages. The exchange of peace “could have gone on for an hour,” she said.

“We all knew what we were saying, and we meant it,” she added.

The archbishop also spoke to the pilgrims, and encouraged them to make the most of their pilgrimage, which involves sacrifice. During a pilgrimage, Catholics are focused on their destination, which is a holy place. They leave behind the distractions of home. Life is also a pilgrimage, and Catholics need to focus on Jesus and His promise of eternal life, he said.

Later in the day, the group from Boston University with 15 students and three campus ministers gathered to sing, read scripture and praise God before participating in a walk along the river to the cathedral. They also prayed the rosary as they approached the gothic building.

“The architecture’s awesome,” said Poremoski from Blessed Kateri.

While she was inside the cathedral, she was awestruck at the thought of the thousands of people who had come inside over the past hundreds of years, she added.

“We can’t even fathom how old these places are,” said Ted Fioraliso, a junior at BU.

Fioraliso said he was glad to have the opportunity to attend Mass every day while in Germany. He also attended WYD in Toronto and said the experience is an opportunity to re-examine his faith.

“You’re in Catholic overdrive,” he added.

Boston travelers celebrated Mass together at St. Andreas Church in Cologne before heading out to Marienfeld, the stretch of farmland where the Papal Mass was celebrated on Aug. 21. Buses dropped them off in a sea of people, several miles from the site where Pope Benedict would lead a prayer service and celebrate Mass.

After a long walk, they discovered that their assigned area was almost completely full and were forced to split up into their smaller parish groups. Many people who arrived later said they were forced to sit much further away from the altar and large screens where most of the pilgrims were able to view all that happened. Others tried to make space in the section, slowly cramming people as close together as possible. Some who arrived shortly before the vigil laid down their tarps and sleeping bags head to toe along a makeshift walkway in the large section.

Some Boston pilgrims commented that they were unimpressed with the dinner and breakfast that were provided during the overnight vigil, which consisted of a can of tuna with assorted vegetables, bread, yogurt, sausage and a shrimp spread.

During the vigil, some 800,000 youths lit candles and listened as Pope Benedict explained that saints “are the true reformers.”

“Only from the saints, only from God does true revolution come, the definitive way to change the world,” he said during the address, which he delivered in German, English, Spanish, French and Italian.

“True revolution consists in simply turning to God who is the measure of what is right and who at the same time is everlasting love. And what could ever save us apart from that love?” he asked.

Enormous black clouds threatened to soak those gathered, but all passed by without raining a drop. Overnight, the dew dampened sleeping bags of those who did not have plastic to cover themselves, and the temperature dropped to 54 degrees.

In the morning, the sun did not really emerge but lit up the gray sky, making it look like all were enclosed in a huge gray dome. Pilgrims awoke cold and hungry, and long lines were found at the bathrooms and hot chocolate stands.

Most had warmed up by the time the pope arrived to celebrate Mass. The pope addressed the crowd in his homily, asking the young people to become new missionaries in a world that is forgetting God.

“Anyone who has discovered Christ must lead others to Him. A great joy cannot be kept to oneself. It has to be passed on,” he said.

Pope Benedict also warned that religion for some has become a “consumer product.”

“People choose what they like, and some are even able to make a profit from it,” he said. “But religion constructed on a ‘do-it-yourself’ basis cannot ultimately help us. It may be comfortable, but at times of crisis we are left to ourselves.”

The pope encouraged the pilgrims to actively participate in Sunday Mass, the Sacrament of Reconciliation and to build communities based on faith.

“In recent decades, movements and communities have come to birth in which the power of the Gospel is keenly felt,” he said.

That evening the entire group ate dinner at the Düsseldorf hotel with Archbishop O’Malley.

“There’s a lot to be proud of in this room,” Father Tom Dunne, director of the Office of Youth Ministry, said to the young pilgrims.

He commended them for taking the pilgrimage seriously and looking at it as a chance to grow in their faith. Many who have participated in a previous WYD have continued to remain active in their faith, he added.

The final WYD Mass, a celebration with the pope, brings home the universality of the Church in both the present and reaching back through history to the first pope, St. Peter, said Archbishop O’Malley.

“The importance of World Youth Day is helping people to fall in love with the Lord and His Church,” he added.

Father Chris O’Connor, a professor at St. John Seminary and youth ministry advocate, ended the evening by reminding pilgrims that without God we are nothing, and urging them to bring that message home.

“Now we’re heading home to give praise and thanks to Him,” he said. “Boston will be stronger when we go back.”