Joyful, singing crowds were walking through Lisbon long after the opening Mass of World Youth Day 2023 was over Aug. 1. The atmosphere surprised even those that lived in the Portuguese capital throughout their lives.

"All those people are now on the streets, it's really exhilarating! I don't think it will happen in my lifetime again that so many pilgrims come to my city!" Concha Sousa, a Portuguese volunteer of WYD 2023, told OSV News.

Sousa is 26 but never participated in WYD before. But now, when it's in her city, "how could you not," she said. "It would be a sin not to!"

Thousands of young people participated in the opening Mass of WYD in Lisbon. Cardinal Manuel Clemente, the patriarch of Lisbon, welcomed them at the Eduardo VII Parc in the city center.

"Lisbon welcomes you wholeheartedly," Cardinal Clemente told the youths.

In his homily, he described to them how the pilgrims were walking in the footsteps of the Blessed Mother. "Mary set out. A path that was difficult and without the means of transportation that we have available today. She was young like all of you, and had just conceived Jesus in a unique way, which the Gospel recounts," Cardinal Clemente said. "All of you also set out. For many it was a difficult journey due to the distance, the connections, and the costs that the trip required. It was necessary to bring together resources, organize activities to obtain them, and rely on solidarity which, thanks to God, was not lacking."

Youth from all countries of the world except from Maldives arrived in Lisbon for the event, including over 1,300 groups comprised of more than 28,600 individuals from across the United States. The U.S. is among the five largest delegations participating in WYD, which is taking place Aug. 1-6. Most U.S. pilgrims to WYD are young adults between the ages of 18 and 25.

"From near or far, you all set out. It is very important to set out. This is how we should face our own lives, as a journey to be traveled, making each day a new segment," Cardinal Clemente said.

Joseph Vo set out to come to WYD from San Jose. He saw the videos of WYD in Krakow in 2016, and that's when he first dreamt of coming to World Youth Day.

"I was 11 at the time, and it was just so beautifully done and inspiring, and with Pope Francis being such an inspiring pope I decided that when I would get older I would one day go to World Youth Day," he said.

He loved the Lisbon encounter from the first sight.

"It's been fantastic, it's been beautiful," he told OSV News. "There is plenty of time to pray and encounter God directly. Also it's just a really beautiful opportunity to talk and engage and meet other young people."

"It feels like we're all family members that haven't seen each other for a long time," Vo said.

For youth, often closed in their own virtual circles, what matters in WYD is the actual personal meeting.

"Virtual reality keeps us seated in front of means that easily use us when we think we use them. Quite to the contrary, reality consists in going out to encounter others and the world as it is, both to admire and make better," Cardinal Clemente said.

"I've never seen so many different people so happy together," a 16-year-old-Portuguese pilgrim said, marching with her friends.

There are 354,000 pilgrims registered for the event, with the most representatives from Spain (77,224 young people), Italy (almost 60,000) and Portugal (43,742). France brought 42,482 pilgrims, followed by the U.S. The theme of WYD is "Mary arose and went with haste."

"When I told Pope Francis that this was precisely the motto of our World Youth Day -- Mary arose and went with haste... -- he immediately added that, 'yes, with haste but not anxiously,'" Cardinal Clemente told the youth at the opening Mass Aug. 1.

The encounter is also important for bishops from all corners of the Catholic world. Almost 700 bishops are registered for the event, according to the organizing committee, 30 of whom are cardinals.

Bishop Artur Wazny, auxiliary bishop of Tarnow, Poland, is one of them, and he told OSV News that after participating in several World Youth Days, this one means a lot to him as it is the first one he is participating in as a bishop.

"Starting with quite a difficult journey, I am really happy I could experience the event just like the young people and with them," he said. "Young people give light and joy, and we can all embrace that joy from them and believe, thanks to them, that what I do as a bishop makes sense. They teach me to be a better man."

"In fact, every meeting we have must begin with a true greeting, in which we exchange words of sincere welcome and full sharing," Cardinal Clemente told the youth.

And the youth don't have to be asked twice. Across Lisbon, they are exchanging signatures on their national flags, taking pictures together and sharing stories, ready to make the most of the next few days together.