NEW YORK — The New York City cultural apostolate Catholic Underground is a success by any measure. Take numbers. Close to 700 people, overwhelmingly young adults, attend the first-Saturday event each month.

And if money is your measure, Catholic Underground wins there too. In addition to individual gifts (including a significant $12,000 gift from a single donor) attendees’ donations and alms have paid for vital repairs at Our Lady of Good Counsel, the hosting parish, and help to support the friars’ work with youth, the homeless and the poor.

But for Brother Louis Marie, the Franciscan Friar of the Renewal who spearheads the events, there is only one meaningful measure of Catholic Underground’s success: the number of serious, deeply felt confessions made at every monthly gathering.

“By that measure, we’re very successful,” he said. Indeed, as many as 15 priests remain throughout the evening to ensure that every person who wants to receive the sacrament may do so.

The Catholic Underground, which begins at 7:30 p.m. and ends at 10:30 p.m., has a two-part format.

The first is Eucharistic adoration and Vespers. With lights and candles focused on a golden monstrance, the darkened church highlights Christ’s presence as a friar leads the chant. After Vespers, the brothers lead the gathering in a Eucharistic meditation accompanied by music. The holy hour concludes with a solemn Benediction.

Seeking to respond to the call to evangelize the culture, the friars use the second part of the evening, in the church basement, to showcase Catholic performing artists. The entertainment can be anything — music, drama, dance, film, even poetry.

The gathering ends with prayer. Everyone joins in chanting Compline (Night Prayer); the evening concludes with a hymn to Our Lady, Daughter of Zion, Mother of the New Jerusalem.

Catholic Underground is a relatively new apostolate. The early gatherings were little more than First Friday get-togethers of music followed by a talk in an unheated church basement.

When the event expanded to include a Eucharistic holy hour, the friars moved to Yonkers’ St. John the Baptist Church. More and more people came, some from as far away as New Jersey and Pennsylvania.

By the mid 2000s, Brother Louis Marie, by then a professed friar, was convinced that Catholic Underground was ready for prime time — in the Big Apple. The need for a venue to hold the gatherings prompted a call to Father Kazimierz Kowalski to ask if his church might be available.

“Yes!” was the immediate answer. “Come!”

“I love having the CFRs around our parish,” said Father Kowalski. “They’re joyful, fun, happy brothers and priests — and they’re completely faithful to the magisterium.”

The last point is particularly important to him. Father Kowalski is a former Lutheran pastor who “swam the Tiber” two decades ago.

Once the date of the first event was set, an extensive announcement campaign was launched via Internet. But the day itself — a drizzling, raw Labor Day weekend in 2006 — wasn’t auspicious.

“That’s why we were so amazed. Over 400 people came,” Father Kowalski recalled.

And they keep coming, every first Saturday, September through May.

Why?

Sarah Gallick, author of The Big Book of Women Saints, may have put her finger on it. “Two things deeply impressed me the first time I went,” she said. “One is spiritual: the sheer awe and humbleness of sitting in that grand old church in silence and semi-darkness, focusing only on the Eucharist. The second is worldly: a good 90% of the crowd is under 30.”

A middle-age Jewish man who tagged along with a Catholic friend called the service the most moving prayer experience of his entire life. Asked about the music afterwards, he demurred. “It was a little too loud for my taste,” he admitted.

Kevin Staudt, a recruiter for Wall Street, agrees about the prayer experience.

“It’s so compelling — very reverent, solemn and peaceful — that people come for the prayer as much as for the entertainment,” he said. Another plus: “It’s an opportunity to hear and enjoy different music.”

Nona Aguilar is based

in New York.