There are snakes in the long grass ahead, Amy, our guide, warns us. She begins to clap her hands and yell. I don’t need much convincing to do the same. Five minutes earlier, I had seen a black serpent coil in and out of an ancient preRoman wall. The slithering from one orifice to another seemed to take a long time; I reckon the animal was close to three feet long. I clap with flamenco-esque fervour.

We are approaching a lost Roman amphitheatre, built up in the hills above Lake Bolsena about the same time as the Colosseum was being constructed. There, the similarity ends. This amphitheatre is tiny in comparison, its framework hidden by a perfect oval of trees and shrubbery. To expose the remnants of the stone benches, you have to high-step through the long grass like a Lipizzaner, shouting as you go, just to warn the jittery snakes. Neglected it might be, but, nevertheless, there is an atmosphere to the place, and it isn’t difficult to imagine that, with a bit of effort, it could be an attractive extra to the town of Bolsena’s attractions. Concerts or fairs might even be held there.

As if. You see, there is another snake in the grass when it comes to visiting Bolsena, the volcanic lake’s main settlement. As a town, it simply isn’t good at all that tourist malarkey. It’s why there are no signposts to the Mercatello amphitheatre, and why only a tiny percentage of visitors will even guess at its existence or at the presence of the overgrown Roman roads with their slablike cobblestones that crisscross the hills around it. Okay, it’s not the Colosseum, but it’s worth a look. A sign can’t do any harm, can it? Apparently so.

There are other indicators of this indifference to the outsider’s needs. On its doorstep is one of the most wondrous sights in northern Italy, the long-abandoned town of Civita di Bagnoregio, clinging to a domed hilltop, reached by a long and steep causeway, its insides medieval-film-set perfect, the views over the scoured moonscape valley magnificent. The surrounding soft, easily eroded rock and a few hefty earthquakes accounted for the desertion of the city. Even today, only about 20 people live there all year round, although artisans and artists take up residence in summer. So, there must be regular shuttle buses from Bolsena to this marvel? Have a guess. “Maybe in August,” I was told.

Bolsena has a Roman town, Volsinii, which, again, might not rival Pompeii, but is worth an hour of anyone’s time, with its ruined villas, forum and basilica (and more snakes, but at least the grass was cut there) and Etruscan wells and tombs. And it’s free. And pretty much empty, because it isn’t promoted. During my visit it seemed the town tourist office had taken a vow of omerta, such was its enthusiasm for imparting information or suggestions.

I could go on, but you get the picture. I met several holidaymakers who were infuriated by this lack of infrastructure and, for the first few hours, planning my whistle-stop itinerary, so was I. My whistle, it appeared, would have to remain mostly unblown. Then I got to nearby Orvieto (the only bus is in the very early morning, so I joined an organised tour), and lovely though it was, I scuttled back to Bolsena and metaphorically slammed the door behind me.

I last saw Orvieto 20 years ago or more. Then, I thought it charming; the city, and especially its cathedral, is still stunning, but the streets are now infused with the whiff of cynicism, of a place that sees too many tourists too often and wants to take their money before they run. It is not in the same league as, say, rapacious San Gimignano, but the rot is perceptible nonetheless.

I began to be grateful for Bolsena’s lack of guile and industry when it comes to tourism. It is why a cup of coffee in Orvieto costs three times as much as on the lakeside at Bolsena, why the waiters there mostly don’t speak English, but serve you simple, good food (if you stick with the lake fish) at knockdown prices and with a smile. It’s why Bolsena’s medieval lanes are quiet even in high season, why the small beaches of volcanic sand are relatively uncrowded while the filthy Med heaves, why you can stroll at twilight beneath the reed arches on the shoreline, listening to bumptious amphibians and marvelling at darting fireflies, and not see another soul.

I asked Amy, the guide, if I had this all wrong. She is English, married to a local, and runs a number of free, three-hour guided walks for guests of the tour operator Inghams, to help them explore the medieval, Roman and Etruscan heritage of the town. But she is also a plain-speaking Yorkshire girl, who tells it straight. Was I being overcritical? Not really, she admitted.

She gave me another example of missed opportunity. Out of the lake juts an island of volcanic material, a plug called Isola Bisentina. It is peaceful, attractive and has a fascinating history – once a summer home of the popes, with a monastery, church and seven chapels – but you can’t go to it. You used to be able to, but the owner of the island suggested that the man who ran the boat trips should help pay for the upkeep of the landing stages, whereas he thought it was the owner’s responsibility.

So no tourist can set foot on beautiful Bisentina until the dispute is settled. This being Italy, it might take a while for such a feud to be resolved.

If all this seems a little negative, let me assure you I now feel an almost pathological fondness for the place. If I could, I’d give Bolsena a cuddle for being so wilfully and refreshingly obtuse. Once I had adapted to the rhythm of the town and accepted that I wouldn’t be covering every possible tourist attraction in the area (did I mention there is no car hire in town?), even though it is brilliantly located for exploring both southern Tuscany and Umbria, I settled back to relax. It isn’t difficult. The light thrown by the mountain-ringed lake (the cleanest in Europe, so they claim) is really quite magical, offering quicksilver days and dazzling sunsets, followed by soft, velvet twilights, to a soundtrack of the ubiquitous frogs (and maybe the thwack of table football from the cafe by the port). And, unlike other Italian lakes, its shores are not defaced by tiers of holiday homes.

Bolsena does have its high days, when the place gets a little crowded. The most visually spectacular celebration is Corpus Christi, or Corpus Domini (this year’s has just taken place; next year’s will be in late May), which, although a nationwide celebration, owes its origins to the miracle of blood spilling from a communal wafer and staining an altar in Bolsena’s main church. The town marks it with a million flower petals, used to create the infiorata: fantastical biblical and sometimes voluptuous images on the streets, a mayfly of floral art, doomed to be trampled to mush by the evening’s procession.

There is also an indigenous saint/martyr to be celebrated, a young Roman Christian convert called Cristina, who was done to death, although she demonstrated more tenacity than Rasputin, surviving being tossed into the lake by her father, boiled alive, put on the rack, whipped and bitten by snakes. She was eventually dispatched, St Sebastian-style, by multiple arrows.

During the Misteri di Santa Cristina, celebrated on July 23 and 24, these various torments are depicted in a series of tableaux around town. A few times each hour, the curtains are drawn back to show the villagers in frozen poses, before they are whisked shut again to allow the actors to grab a quick cigarette and a glass of the local Est! Est!! Est!!! wine (far less exciting than the exclamation-heavy name suggests). Only the clutch of adolescents chosen to play Cristina changes each year: the tradition is that once you have a place in a particular tableau, it’s yours for life. There are some people on stage who’ve been torturing the poor girl for 60-odd years now.

On my final day, I walked along the western shore of the lake, heading for Capodimonte. It’s just over 15 miles from Bolsena and, once you get off the main road, tranquil and lovely. Frogs and birds abound, and fish can be seen darting through the almost unnaturally clear waters. Capodimonte itself is a pretty, sleepy town on a promontory that juts out into the lake (it does not make the hideous pottery, that’s Naples). After a long, hot stroll, I stopped at a cafe at the lake edge for water and a coffee, the only customer.

When the waiter delivered the drinks, he asked me where I was staying. Bolsena, I told him. He gave me a pitying look. It gets very busy over there, he said, too busy. I looked carefully into his face for signs of irony, thinking he was joking. He wasn’t. I finished my coffee, left a tip and, with the sun beginning to fall and the frogs clearing their throats for the coming performance, I ordered a cab to take me back to the seething fleshpots of Bolsena.

Rob Ryan travelled as a guest of Inghams. His latest novel is Dying Day (Headline £11.99)

Travel brief

Getting there: Bolsena is two hours’ drive north of Rome. The city is well served from many regional airports, as well as London, by Air One (020 8939 2434, www.flyairone.it), Alitalia (0870 544 8259, www.alitalia.com), BMI Baby (0871 224 0224, www.bmibaby.com), British Airways (0870 850 9850, www.ba.com), EasyJet (www.easyjet.com), Ryanair (0871 246 0000, www.ryanair.com) and Aer Lingus (0818 365 000, www. aerlingus.com). From Rome, you can travel by rail to Orvieto and catch a bus to Bolsena, but car hire is probably best. A week through Holiday Autos (0870 400 4447, www.holidayautos.co.uk) costs from £140.

Where to stay: the Royal (00 39-0761 797048, www.bolsenahotel.it) is the best hotel in town, comfortable and central; doubles from £66, B&B. The Hotel Holiday (0761 799079, www.hotelholidaybolsena.it) is a short stroll outside town, modern and friendly, with some lake-view rooms; from £40, B&B.

Tour operators: Inghams (020 8780 4433, www.inghams.co.uk) has a week at the four-star Hotel Royal from £514pp, half-board, with packed lunches and two optional three-hour guided walks (£1 registration fee). This includes return flights with British Airways from Heathrow to Rome and resort transfers, with regional flights available for a supplement. Three- and four-night breaks are also available. Travelsphere (0870 240 2426, www. travelsphere.co.uk) runs holidays to the area; and ATG (01865 315678, www.atg-oxford.co.uk) features some time in Bolsena in its walking and cycling holidays. Sunvil (020 8568 4499, www.sunvil.co.uk) is the booking agent for photography courses run by Paul Harcourt Davies in the countryside between Bolsena and Orvieto.

Best guidebook: Bolsena: Everything You Need to Know by Fleur Kinson (Norzia Press £10.99).

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