You could visit St Mary without ever seeing Wortham - and vice versa. The parish contains five settlements scattered around Suffolk's largest common. The biggest village is on the main Bury to Diss road, where you'll find the pub and a lovely old-fashioned little shop-cum-cafe. St Mary, by contrast, is on its own a mile or so to the north on an ancient road that runs between Palgrave and Redgrave. Between the church and the village stretches the ancient common, gorse-covered now that it is undergrazed, bleak and mysterious in winter, verdant in summer. It's a strange place. St Mary has the biggest round tower in England, fully ten metres across. Round towers are an East Anglian speciality, apart from a handful in the Ouse valley in Sussex, and the source of some wild speculation. The Saxon origins of some have encouraged people to suggest that they were fortifications, and only had churches added to them when the Normans came.

However, many of the round towers post-date the Norman Invasion - indeed, some seem to be from as late as the 13th Century - and some of them are not as old as the churches against which they stand. Bramfield is the only one in Suffolk that is separate from a church building, suggesting that they were always ecclesial in character. The most outlandish explanation is that they are the linings of ancient wells, left exposed as the land receded. This is pure nonsense, of course, but rather charming. They were all probably built as church towers, and may have been intended as lookout towers as well (why not? we know that some of the square ones were). But it is hard to look at the mighty bulk of Wortham tower and not think that it had some kind of defensive purpose as well.

I fondly remember being here on a lovely day in early summer. I had cycled the four miles from Palgrave along the narrow lane in a shimmering heat. There were no cars about, not a person to be seen. A huge golden hare sat watchfully in the verge, hauling himself back into the hedgerow as I approached. Off to my right, a line of low hills was punctuated by church towers, one of them round and only a field or so away; but they were all in Norfolk. Most recently, Peter Stephens and I came here on the day of the 2008 Historic Churches Bike Ride, another beautiful day, when the lanes were full of life.

St Mary's tower is so striking that it might take you a moment to notice quite how lovely the nave is. It has one of the prettiest clerestories in north Suffolk. The setting is lovely too, within a mature graveyard that is maintained as a wildlife sanctuary. Although you can't go inside the tower, you can see inside. It is open to the sky, but you can make out where internal floors were, and what looks like a fireplace. If the tower predates the Normans, then it doesn't do so by much. The little bellcote was added in the 18th century, presumably because the internal floors of the tower had collapsed.

The rest of the building is almost entirely the result of energetic activity in the half century or so after the Black Death. This is when the aisles were added, and then the clerestory and chancel. You step inside to a welcoming, well-kept interior. It doesn't feel particularly rustic; we could be in the middle of a small town.

I hope you will be as struck as I always am by the bench ends. They were done by a parishioner, Albert Bartrum, in the 1890s. They illustrate the verses of the 104th psalm, and as well as various figures going about their business they include a walrus, a tortoise and an owl. A bench in the south aisle has blacksmiths tools carved on it, perhaps to remember someone who once regularly sat there.

Much of the interior furnishings were renewed as part of a series of vigorous restorations during the second half of the 19th century, mostly under the eyes of one of Suffolk's most famous ministers, Richard Cobbold. He was Rector here for more than 50 years, and completely oversaw the turnaround in the Church of England that transformed St Mary from a preaching hall to a sacramental house of God. He is more familiar to historians as the author of the notes that became Biography of a Victorian Village, probably the best single account of Suffolk in the 19th century; now incomprehensibly out of print, although easy enough to obtain second-hand. Because of it, we know more about Wortham in the 19th century than any other Suffolk parish. He also wrote the novel Margaret Catchpole, a best-seller in its day, and still worth a read. This novel is remembered in the name of the pub beside the grounds of the former Cobbold family home in Cliff Lane, Ipswich. Cobbold himself is remembered by a modest memorial on the chancel wall, that's all.

The font he baptised several generations of his parishioners in is a fat 14th century one, with grand traceried gables on the panels. There is an unusual carved Charles II royal arms, nearly identical to a set in the church of the neighbouring parish of Mellis. A more recent arrival is a set of four glass medallions illustrating the seasons; they are not to my taste, but they are a sign that this church is still renewing itself.

A lovely building, then, and about halfway between two others that are equally lovely, so if you fancy a nice bike ride I recommend you to take your bike on the train to Diss, cycle a mile or so to Palgrave, and then along this narrow lane past St Mary to Redgrave. Not only will you have visited three fine churches, but Redgrave has a decent pub. A stop there may refresh you enough to allow you to continue through Hinderclay, Hepworth, Walsham, Ixworth, and all the way to Bury St Edmunds, where your train awaits. Not far from the churchyard, along the road to Redgrave, a modest memorial sits by the corner of a field. It remembers the tithe wars of the 1930s, when non-churchgoing landowners fought for the right not to pay for the upkeep of the local established church. One of the biggest confrontations was here at Wortham, where there was a stand-off between hundreds of police and fascist black-shirt thugs outside Wortham Rectory. Hard to imagine now.