This is a tale of two visits - a tale of two churches, even. The vast majority of East Anglia's churches are open and welcoming to visitors, strangers and pilgrims every day, but some are not. A small minority of those which are not do not even have a notice telling you where to get the key, or advising you to turn up between 9 am and 10 am on a Saturday morning (I kid you not, there really is one in Norfolk like that). These churches return a blank stare to your hopes. In the years I've spent travelling around Norfolk and Suffolk, I've began to think of them as fortress churches. To qualify as a fortress, a church has to be impenetrable to me on more than one occasion, and to other people I know, or who have contacted me about it. It helps if the church had a particularly unwelcoming aspect, like an ugly padlock and chain, or a lack of friendly notices. Great Cressingham church qualified on every count, which was a great disappointment, because it is a building of some importance.

But I always journey with hope. This is because I have been visiting churches long enough to know that circumstances change: churchwardens change, or have changes of heart, or have their hearts changed for them by enthusiastic incoming incumbents.

Something has changed at Great Cressingham, and I am delighted to tell you that it is now possible to visit this big, fascinating church. This is a story in two parts, then: the before and the after, the old and the new, the darkness and the journey into the light. But first, this is what I wrote a little over a year ago, when things were not so bright.

2007:There is something poignant about the photograph at the top of this page, because as you can see this is a quite magnificent building, a great 15th century Perpendicular rebuilding of what must have been a very fine 13th century church, from which the pinnacles at the east end of the chancel survive. The chancel in particular is a delight, with those beautiful windows ranging on the north and south sides. We came here in the spring, and the graveyard was lovely around the mighty pile. The tower is formidable, a powerful structure telescoping skywards, crowned by 20th century battlements and pinnacles, proud and glorious. The porch is big, but dwarfed by the hugeness of the building against it. The remains of a late medieval statue of St Michael are in the niche above the entrance. All in all, a fitting church for its bold patron Saint, who is recalled by the monograms around the base of the tower.

What it is like inside I cannot tell you, and no one else has been able to tell me. Great Cressingham is, I am afraid, one of the least welcoming churches that I have visited in East Anglia. An ugly metal chain and padlock are stretched across the medieval doors, a latch screwed into the ancient wood. At first, I wondered if the church had fallen into disuse, but I could not believe that a village the size of Great Cressingham could not support a parish church. And in any case, the building must still be in use for something, for a noticeboard beside the door had a laminated card typical of the early years of the 21st century: Caution, uneven floor, danger of tripping. I wondered at first if the whole building was such a hazard that the churchwardens didn't dare risk anyone else entering, for fear that those wolves and leeches of the modern age, the no-win-no-fee solicitors, would descend, to tear the PCC to pieces, or to suck it dry for compensation. But as it turned out, this is an unlikely reason.

Great Cressingham is one of the Wayland Parishes. A great injection of European money was made in the late 1990s to try and revive the economy in this, one of the poorest parts of East Anglia. Mostly, this has been very successful; the Wayland Initiative has brought new life to the town of Watton, lifting it from a moribund state to being a lively, pretty place again. Part of the initiative was to encourage tourism, and the local authority worked with the area's parish churches to develop church trails, tours and the like. It is possible to walk into the office in Watton, and they will tell you the interesting features of each church, where to find a key, and who to contact if you want to be shown around. Except, unfortunately, at Great Cressingham. They're a funny lot up there, the lady in the Wayland Initiative Office said. They just don't like people going inside.

This is bad for all sorts of reasons. For a start, it means that the parish simply isn't doing its job. Christ's injunction for us to welcome the stranger within the gate is hardly fulfilled by this ugly lock and chain. I wonder how a foreign visitor might feel, returning to the parish of his ancestors, hoping at least to see the War Memorial inside the church. And I know that this building has medieval survivals in the form of some interesting glass, but it is not considered that you and I should see them. I wonder if the parish has received any public money for the upkeep of the building? It should be a condition of all grant aid that the church is accessible to the public at all reasonable times.

It may well be that Great Cressingham is a thriving parish, and this church is packed to the gunwales three times every Sunday. Perhaps they actually don't need to be open as an act of witness to strangers, pilgrims and those with a thirst for a sense of the spiritual. Indeed, perhaps they have no room to welcome the tax collectors and sinners who might respond to the sense of the numinous they'd find by wandering into this building on their own, on a weekday.

But I suspect that this isn't so. The great majority of Norfolk's medieval churches are open to visitors every day. The Church of England knows the power of an open church, knows that it is its greatest act of witness, and in any case works very hard in this county ministering to all its people, Christians or not. But there are still pockets of Norfolk where the buildings are kept locked from one end of the week to the next, where the risk of Faith that an open door represents is not taken.

Instead, such benefices open their churches only for the slightly smug activities of the Sunday club, while the graveyard is left to the pagan cult of the dead, the bereaved worshipping their recent ancestors with propitiatory flowers, unable to combine this with a prayer said inside a sacred building, increasingly unaware even that this might be an appropriate thing to do.

As the years go by, the congregation gets smaller, and older, and less welcoming to strangers, hanging on to the rituals that comfort them but which otherwise serve no community devotional purpose, and are no means for sharing the faith and love and life of the parish. The building is used less and less often, eventually being abandoned altogether by people who, no doubt, bemoan the decline and fall of their congregation and shake their heads gravely at the immorality of the young of today, their lack of respect and belief.

And yet, they have not even once taken the risk of letting themselves be found by us, the strangers wondering at the God-shaped hole within ourselves, surprising a hunger to be more serious, and gravitating with it to this ground.

I may well yet be told that the parish of Great Cressingham is not at all like this. But I expect that it probably is. The medieval parish churches of England belong to all of us, and if the current financial arrangements mean that too much responsibility falls on the local community, then those arrangements need to be changed. What does this locked fortress tell us about the hearts and minds of Christ's Church in Great Cressingham? Are we not to be trusted to enter the House of God? Ironically, the noticeboard beside the south door is headed CIVIL NOTICES. The most civil notice I could think of would be one that showed the times that the church was open, and where you could get the key when it was not.

But in the event, none of this was necessary. Thinking that we would look fairly foolish if we went hunting for a key when the church, by some unlikely eventuality, had been open all along, I went up to the south porch to check. The big padlock and chain were still in situ, but there was something new. On the Civil Notices board there was a small laminated notice reading A key to the church is available from the following, and underneath it were three names and telephone numbers.

Now, it would be false modesty for me to suggest that I didn't wonder, for a moment, if this was a result of what I had written about the church in 2007. However, I don't think so, because if that had been the case then I have no doubt that they would have contacted me to tell me so (people do - a couple of dozen times I have moaned about an inaccessible church, only to have a cheery warden contact me to say that there is now a keyholder notice), and I thought that it was probably something to do with that hoary old stumbling block, Health and Safety. Although I do not believe there is any legislation on the matter, churches are advised to put up a notice explaining the exact location of the building in case someone on the premises needs to call the emergency services, and a contact telephone number if access to the church is needed in an emergency. The fact that these were telephone numbers suggested that this was probably the reason, although curiously the names did not appear to match up with the churchwardens in the Diocesan Directory. I rang the first number on the list, more in hope than expectation. It was the middle of the morning on a weekday, and I thought there was a fair chance that nobody would be in. I let it ring, and it rang and it rang - and then it was answered, by a rather breathless voice which listened to my request and then very politely said to wait a couple of minutes and he'd be over with the key. I have to confess that I expected a rather doddery old chap to appear, but in fact he was a jolly, rather hippyish man dressed in bright clothes who explained that he had been moving a heavy bed. He seemed genuinely pleased that we wanted to see inside the church. He unlocked the padlock, asked us to close it up again when we had finished, and left us to it.

When I'm about to step into a church which I've never been into before, especially when it seems against all the odds, a kind of Howard Carter-at-the-tomb-of-Tutankhamunish feeling comes over me. We stepped into a large, open space which was far lighter inside than the gloomy day outside. A forest of arcades lifted the roof above the clerestory, and led the eye to the vast chancel, the great east window flooding the building. It was rather breathtaking.

The great treasure of the church is the range of 15th Century glass in the north aisle. There are remains of three sequences. Firstly, a group of six Bishops, similar to those at Wiggenhall St Mary Magdalen in the far west of Norfolk. They are obviously the work of the Norwich school. Next to them, and also the work of the Norwich school, are six angels. The two outer pairs reflect each other, one pair being reversed. There are six more angels in a further window, and together they represent three of the orders of angels. Finally, in the top lights there are three figures which appear the same at first, until you see that one is a fragment of Christ at the Resurrection, leaping from his tomb (there is one very similar at Blakeney), another is Christ at the Coronation of the Blessed Virgin, and the third appears to be Christ in Majesty. They are three parts of a rosary sequence, the Glorious Mysteries.

While the glass at Great Cressingham is not well-known, even more of a secret is the fact that this church has no fewer than five figure brasses, with the inlays for a couple more. They are all late medieval. The two best are probably those for Thomasina and Richard Rysle, who died in 1497. These 45cm figures are perfect miniatures. Twice as tall is William Eyre, who wears a colar with IHC on it. His wife's figure is now missing, as is another figure which must have been a mourning son. Very curiously, the inscription underneath has been trimmed at both ends, probably as a result of the two figures being removed, but also possibly to remove the Catholic prayer clauses. The best of the figures, though, is the Priest John Aborfeld, in full eucharistic vestments of the early years of the 16th century, when time was running out for the English Catholic Church.

Above all this, the nave roof is beautiful. It is late medieval, probably from the last years of the 15th century, and is supported by alternating hammer beams and arched braces. The large figures appear to be Priests (one of them is a Bishop) with angels beneath. A delightful touch is the pair of figures hard against the east wall of the nave. They are suspended above where the great rood would have been in medieval times, the representation of Christ crucified flanked by his mother and St John. The two figures extend their hands in the gestures that you can still see a Priest enact at the consecration of the Eucharist in any Catholic church in the world today.

I mentioned before that the great Perpendicular east window fills the chancel with light. You step through the screen to discover that it is, in fact, an interloper, and this is still largely a chancel in its late 13th century integrity. It must be one of the biggest of its date in East Anglia. Great blank arcades line the sides, leading the eye to the altar. Curiously, 17th and 18th century memorials to the Lobb family are set directly on the pillars of the arcade on the north side. On the south side, a curious sight, a memorial which has fallen, or been removed, leaving only the signature of the mason and scraps of what look like a 1970s tabloid newspaper pressed in to help a temporary repair at some point. This is remarkable church, and deserves to be so much better known. I sat down and wrote a near-essay in the visitors book, in the hope that they will know how much their change of heart is appreciated, and a plea to please, please, please leave the church open during the day, at least in summer. In the long term it will make it so much safer against vandalism, and who knows? the parish might even win a few new members.