For our holidays For our holidays For our mountain bike holidaysThere was an elegant simplicity to Zarko Bartolic’s beige 1982 Renault, a battered four-door that — if I succeeded in deciphering his Slav-accented Italian with my rusty Utah Spanish — was paid for entirely with money he earned finding truffles in the Croatian mountains and selling them to local restaurants.We were speeding along through the mountains near Zarko’s home on the Istrian peninsula, and the cool morning air that came rushing in through his improvised and very direct cooling system (a large hole in the dashboard) was precious relief to our little party; our weeklong mountain-biking trip through this slice of northwestern Croatia last summer had coincided with a brutal heat wave.

But now we were rolling through the vineyards and hazel trees, and as the breeze circulated through the car, we all smiled at the half-suppressed yelps of Zarko’s dog, Nero — he could barely contain his eagerness to hunt some truffles. Even the body of the ancient Renault seemed to squirm with anticipation, doing a little shimmy as it resettled itself after each big turn.

In a way, it felt like cheating. Our original plan had been to mountain bike through the peninsula, but we hadn’t counted on the 97-degree heat and high humidity, so we were limiting our bike rides to the early mornings and evenings, saving the middle of the day for auto-borne adventures like this one. (Spring, early summer and early fall are the best times for biking through Istria, when temperatures usually range from the 60s to the 80s; the place heats up in July and August, though that remains the busiest tourist period.)

When it broke off from Yugoslavia in 1991, Croatia took with it more than a thousand miles of coastline, and more than a thousand islands, the majority of which are uninhabited.

It also got Istria, a cone-shaped peninsula that juts off Slovenia and tapers to a point about 40 miles into the Adriatic Sea. It is a land that inspired James Joyce and Jules Verne, and was rediscovered by tourists only after the Croatian war for independence ended in 1995.

Most visitors stick to the coast, where villages teeter on limestone peninsulas, the pastel walls of the outermost buildings dropping straight down to the surf. But there is an overlooked magnetism to Istria’s uncrowded interior, with its diverse cultural influences and medieval villages perched on fortified hilltops.

One good way to appreciate hauntingly beautiful villages is to link them together in a mountain bike tour, traversing Istria one village each night. On a bicycle, one can cover the same roads the Romans, Hapsburgs and Napoleon used. There is an entire network of red-dirt paths through fallow hayfields and stands of scrub oak reminiscent of Southern California. Carry only a trail map, water and tire repair kits; it isn’t hard to find locals willing to transport luggage from hotel to hotel.

The terrain is easy enough. For us, in fact, the most technical part was picking our way through the maze of beach resorts and mega-campsites outside Umag, the gaudy town where most Istria trips begin. There, nude Germans were smoking cigarettes in the blazing sun while their children went wild out in the lagoon, climbing up and throwing their peers off massive inflatable rafts designed to look like icebergs.

But as soon as we turned inland, we were surrounded by peaceful Mediterranean pine forests and cornfields. The trail followed every type of lane, from narrow paved roads to smooth dirt paths along the edge of hayfields. Soon we were on the network of official bike routes that crisscross the peninsula — scenic loops that are marked by unobtrusive painted signs.

There is a monastic silence in the small, ancient towns of inland Istria, where shards of dusty white limestone crunched under our tires and echoed down the narrow alleyways. Black-clad old women made their glacial way home from spare Catholic churches, and no matter how much we slowed our pace, it still felt rowdy and uncouth to roll by on our 18-speed, mechanized contraptions, tricked out with shock-absorbers and garish paint.

In this way, we immersed ourselves for several days in the haunting isolation of inland towns like Grascice, Groznjan and Oprtalj. These towns often seemed utterly deserted as we arrived. Riding under an archway through Grascice’s crumbling walls, for instance, it seemed that the bed-and-breakfast where we planned to stay that night was the only game in town. But during our patio dinner of veal cutlets and honey-flavored grappa, we noticed ghostly murmurs coming from the courtyards behind the walls: the town was inhabited after all.

Such evenings were the best time for getting on our bicycles and taking short tours of the area, looping through the vineyards outside town as the days cooled off. There were silent old men sitting by the roadside, watching the world go by. Each traveler on the road got a long, poker-faced study from the old men, whether it was a carload of teenagers with Italian hip-hop blaring from their hatchback, or a Lamborghini tractor hauling a load of corn.

Next we visited Motovun, the most celebrated of Istria’s interior towns. One reaches this town by a narrow road that spirals upward around a steep mountain. Quiet and spare, Motovun has a few tasteful shops, some grand horse chestnut trees and some fine patio dining at the Hotel Kastel, a lovely 17th-century building on the very peak of the mountain, where we spent the night.
The Istrian Peninsula

Throwing open the tall windows to catch the breeze, we looked out across the long valleys to see Oprtalj, the mountaintop village where we’d spent the previous night. Children, calling out to each other in Italian, were playing soccer in the modest town square. Motovun is the birthplace of Mario Andretti, the auto-racing legend, and the town was named Montona d’Istria when he was born there in 1940. Mr. Andretti was among tens of thousands of Istrians of Italian heritage who left the country following World War II, fleeing from reprisal killings conducted by Yugoslav partisans against perceived supporters of the Axis powers. (Italy’s Fascist government had controlled Istria since the First World War, and had enforced a campaign of Italianization on the region.)

The exact numbers of people who were executed or became refugees in the late 1940s is widely disputed. The most notorious of the atrocities were known as the foibe massacres, in which thousands of ethnic Italians were killed and thrown into foibe, or sinkholes.

Such convulsive violence is an old story in Europe, but it was hard for us to fathom such events as we sipped cappuccino under the grand old horse chestnut trees that shade the upper reaches of Motovun.

It was there that we met Ronald Geul, the young proprietor of Barbacan, an astonishing little restaurant and espresso bar. When he asked what was the largest number of truffles I had ever seen in one place, I admitted that until recently I vaguely believed that truffles were endangered forest animals. Smiling wordlessly, Ronald went into a back room, opened a refrigerator and came out with a brown paper lunch bag filled six inches deep with truffles.

A stash like that, Ronald said, was worth more than a thousand dollars. Over the next week, his cooks would shave this batch into gnocchi and pasta, or mix it into wild boar croquettes that he drizzled with horseradish sauce.

“Istrians use dogs to hunt them instead of pigs because dogs are housetrained and pigs will flood the backseat of your car on the way to the forest,” Ronald said, taking a golf-ball-sized truffle from the bag. He held it close to his ear and squeezed it, which he said was a way to listen for worms.

This one was clean. He sliced it open, and an indescribably rich, earthy aroma spread through the corner of the room.

Ronald said Istrians didn’t realize what a treasured resource they had until World War II, when Italian soldiers pointed out the potential. The soldiers themselves are said to have been from similar terrain like Lombardy and Piedmont.

Noting my fascination, Ronald offered to introduce me to his dealer.

And that’s how we ended up with Zarko, parking the old Renault behind a country chapel at the edge of a ravine in the Istrian highlands. Zarko got out a small and well-worn trowel, and led us after Nero, who already had his nose down on the trail.

Over the course of an hour, Nero found about a pound of the precious fungi while being coaxed through the task by Zarko’s steady encouragement — a low murmur of “soo, soo, soo.” Whenever Nero nosed up a truffle, Zarko would pick it from the dirt with his trowel, stuff it in his pocket and feed Nero a treat while exclaiming “Bravo” again and again. Most of the finds were the size of acorns — modest dwarfs compared with the 2.89-pound, football-sized truffle that Giancarlo Zigante and his dog, Diana, found near Motovun in 1999 (winning them an entry in the Guinness Book of World Records).

Now, so many Istrians have embraced the truffle industry that there is a licensing system for hunters. The lust for truffles has led to some territorialist shenanigans, like the poisoning of dogs and the slashing of tires. For the more rare and precious Istrian white truffle, the hunting season is limited to the fall: Sept. 15 until around the time the ground freezes.

A few hours later, Zarko returned with us to his house for truffle omelettes with his family. He refused any payment for the tour and the hospitality, which was done out of pure hospitality and regional pride.

In Istria, crumbling castles and heterogeneous traditions give locals a constant reminder of the successive empires that have fought to control the countryside. In Zarko’s home, we all felt grateful for Istria’s window of marvelous peace.