The Giornata FAI di Primavera, held on 25 and 26 March, began auspiciously with generous lashings of springtime sun bathing the Eternal City. The Giornata FAI is one weekend (and not, as the name confusingly suggests, one day) a year when Italys version of the National Trust (the Fondo per lAmbiente Italiano) opens up sites, monuments and parks across the country, including some that are usually closed to the general public. Entrance is free and guided tours are provided.

This year 410 sites were opened in Italy 27 in Lazio and eight in Rome, including the so-called Palazzaccio in Piazza Cavour and Palazzo Giustiniani, a 16th-century building belonging to the Senate that contains an important art collection as well as the room where the Italian constitution was signed. Over 420,000 Italians and tourists braved several hours of queues to see cultural treasures normally out of their reach.

Organised by FAIs various regional committees, the event is only feasible because of an army of volunteers who pitch in to help every year. This year there were over 6,000 and I was one of them. I offered my services at one of the Rome sites, the Coro Monastico di S. Cecilia in Trastevere, which is attached to the church of the same name in the eponymous piazza. The choir area, located in a gallery above the door of the church and used by the nuns of the still-functioning adjoining convent, contains some of the remains of the Last Judgment by 13th-Century Byzantine painter Pietro Cavallinis. The fresco is a beautiful and luminous work, made all the more remarkable because rebuilding and renovation work in the church over the centuries meant it had got lost behind stalls and panelling and was only rediscovered in 1900.

Though the fresco (unlike many other sites open this weekend) is actually open to the public for a limited amount of time in the mornings, visitors often find themselves faced with a closed door if the nuns have a spiritual retreat or period of prayer planned that day. Hence FAIs decision to open it to all for the weekend.

At 11.00 on the Saturday the queue was already winding its way from the internal cloister right to the back of the square outside. The volunteers were allotted different tasks. One wizened and fortunately humorous old-timer was given the unenviable job of ferrying people up and down from the choir area in a claustrophobic eight-person lift as the nuns had asked us not to use the stairs that lead to the gallery from the church.

Other volunteers manned the information stand where people can also become FAI members, and others were asked to walk up and down the queue selling information booklets, answering questions and generally soothing any frayed nerves. And there were, maybe surprisingly, plenty of these.

FAI members (who are given preferential entry) soon started complaining that the ratio of entrance of members to non-members was grossly unfair. The non-members, on the other hand, kept asking why the queue was moving so slowly. We explained that due to the size of the lift, and the fact that the choir area itself was not very large, the groups were being kept small. But by midday it became clear that the people joining the queue had a wait of at least two to two-and-a-half-hours ahead of them. A decision was taken to make the groups bigger and the queue started to move a little faster: about 20 people got in every ten to fifteen minutes.

At 13.00 however, things slowed down again as the nuns, who are an order in clausura or enclosed, asked to close the choir area (the church is also closed between 13.00 and 16.00) for 15 minutes while they pray. You have to be kidding me? exclaimed one woman. You should have organised things better, she barked. The same combative woman was further aggravated when the 15-minute recess turned into 25 minutes and when she asked for a booklet (containing detailed background information on all the sites open that weekend in Lazio) and was told she had to make a free contribution (offerta libera) of at least 1. Whats free about that? she wisecracked without the hint of a smile. She had a point so I swiftly change my sales pitch to The booklet costs 1, or whatever you feel you can give to support the FAI.

After lunch things calmed down again and at about 15:30 a member of the carabinieri corps joined us with the task of telling people that if they started to queue now they would almost surely not get in. About 150 people decided to queue anyway, including one man who asked: How come Italy has 65 per cent of the worlds artistic treasures but you people are always trying to keep us away from them?

At 17.00 the main gates were closed and only a side-entrance was left open. People could still visit the church until 19:15 but the fresco queue was closed for the day. At some point during the afternoon the nuns had softened and agreed that the gallery could stay open until 18:30, instead of the previously agreed time of 17:30.

As the sun started its descent we told late arrivals to come back tomorrow. One 70-something couple leaving the church was beaming. They thanked us and said: It was a long wait but it was really worth it. And, in turn, their comment made the experience worth it for us volunteers.

For more information on the event, membership and the FAIs year-round initiatives log on to www.fondoambiente.it.