Six members of the Australian Defence Force Academy (ADFA), who visited Brazil and Peru for World Youth Day last month, built a 150-metre-long staircase to replace an unsafe pathway in the area of Pamplona Alta, a slum suburb squeezed up into the foothills of the Andes above Lima.

The group, inspired by the optimism of the people they helped, is already planning their next trip to South America.

Midshipman Gordon Hutcheon, a second-year student, said his first sight of Pamplona Alta had been a revelation.

''The air is polluted and hazy, there is a constant smell of rotting garbage and dead animals, and the houses are built on steep inclines. They are made out of fibro sheets and are only a couple of metres wide,'' he said. ''Everything is very dusty; although Lima is on the coast, it is in the desert. The first thing anyone told us about the place was that it never rains.''

Despite their surroundings, the residents had been welcoming and friendly. ''Many of the houses are brilliantly coloured; they are painted in greens and purple, yellow and orange,'' Mr Hutcheon, 21, said. ''The people we met were not despondent or sad; they are hopeful and were overjoyed to see us. When we arrived they cheered and waved.''

The Canberra group, who also included students from the Australian Catholic University, had volunteered to assist the Fraternas Sisters, a Lima-based Catholic mission.

Their challenge was to build a 150-metre-long, two-metre-wide staircase up a steep slope between two rows of homes. The ground is too steep to walk on normally and the authorities won't put the water on until a neighbourhood is defined by its own steps.

''Even before we had finished the whole group were asking if we could come back and help again,'' Mr Hutcheon said. ''We are certainly hopeful that groups from ADFA will be able to return to Pamplona on a regular basis.

''The depth of this shared experience has brought us closer together.

''While we knew each other (through ADFA) before we left, we didn't really know each other (the way we do now).''

Pilot Officer Ashlea Waight, a fourth-year engineering student, said while attending the first World Youth Day to be officiated by Pope Francis had not been her reason for going, it had made the trip memorable.

''I wanted to get a clearer understanding of my faith,'' she said. ''I am not terribly connected right now and have not been going to church for the last few years.''

She said the atmosphere on Copacabana beach the night before Pope Francis officiated the Mass on Sunday, July 28, had been electric. ''Almost two million people slept on the beach; we had little boxes of food supplied by the organisers and before the Mass began the crowd was chanting 'we are the youth of the Pope' in Portuguese.''

The ADFA students, who paid their own way with some support from Catholic organisations, were led by chaplain Anthony Doyle, an army reservist who works with the ADFA community.

Between 25 and 30 Canberrans travelled to South America as part of the ADFA group.