But as the country prepares for the arrival of the Pope today, the armed men prowling the favela are not the resident drug dealers. They are Brazil's plainclothes federal police officers, and only after they have arrived is it considered safe for visitors to pass through.
"It's peaceful, it's peaceful," a military police officer, who has his blood type stitched into his name badge, said at the entrance to the favela where he is on duty. "But wait 15 minutes, and the federal police will be here."
The first trip abroad by Argentine-born Francis since he was elected Pope in March has aroused huge excitement across the continent where he worked for much of his life - first as a lowly parish priest in the slums of Buenos Aires and ultimately as Cardinal Jorge Mario Bergoglio.
Tens of thousands of pilgrims have begun to descend on Rio, from within Brazil and around the world, to join in the Roman Catholic Church's celebrations for World Youth Day.
Some will be housed in the crowded favelas, the urban shanty towns that are home to hundreds of thousands of the city's inhabitants.
Once a byword for crime and violence, some at least have been partially cleaned up as part of a government drive to rejuvenate the city and prepare it for next year's World Cup and the Olympic Games that will follow in 2016.
The Varginha favela was "pacified" last October, when police occupied the community to try to drive out drugs and guns. A special police unit has now been installed nearby.
Across the main road that runs past the chapel, dust swirls in the air, as a result of demolition in the neighbouring favela where precarious structures have been half knocked down, exposing the insides of some of the poorest homes in the city.
By comparison, Varginha favela looks developed and sophisticated, with its greenery and fresh asphalt specially laid down on the road along which the Pope will walk.
"Go beyond it and it is different," said Paulo Raimundo, 43, president of the residents' association. "Cosmetic changes, little things, for the Pope's visit, are great. But I hope for more, much more. When it was decided the Pope would come here, we were promised many things. But in terms of the big things, the positive legacy, nothing was done."
Pope Francis arrives at a turbulent time for Brazil: in the past month, hundreds of thousands of people have joined unprecedented demonstrations against the lack of investment in public services - in stark contrast to the funds being lavished on the two global sporting events.
People are also angry at the 100 million ($193 million) cost of the week-long programme taking place for World Youth Day, though organisers insist that 70 per cent of the cost has been covered by registration fees.
The Government, led by President Dilma Rousseff, is hoping that the Pope's visit will pass without a repeat of the street protests that brought parts of Brazil to a standstill, but activists have other plans: demonstrations are a certainty, the only question being whether they end with violence.
John Allen, a writer with the US-based National Catholic Reporter and the author of several books on the Vatican, said: "The wild card in all this is, how will the Brazilian street respond to the Pope? People there are angry.
"Protesters want to use the presence of the Pope to concentrate the eyes of the world on the systemic failures of their political class.
"Will the visit be seen as another waste of money, or will Francis be seen as an apostle of the poor, a sort of Che Guevara of the protests?"
The decision to put Varginha favela on his itinerary may help defuse resentment among many Brazilians at the widening gap between the country's richest and most powerful figures and the wider public, struggling to obtain what many now see as their economic rights.
Pontiff's week in Brazil
1 of Rio's more than 1000 hillside shantytowns to be visited by the Pope.
1m young Catholics to gather for World Youth Day festivities.
2 mass events on 4km-long Copacabana Beach.
10,000 police officers and more than 14,000 soldiers will be on duty.
6 Brazilian military aircraft will provide transportation for the Pontiff.
100 lookout towers will also allow police to monitor the World Youth Day's closing Mass in Guaratiba.
US$52m cost of the security and logistical measures for the papal visit.
- AP
