There is a small town in the southwestern German state of Baden-Württemberg, on the banks of the River Brenz near the border with Bavaria.

Heidenheim, population 50,000, is known for its manufacturing industry – machinery, packaging, bandaging, electronics, if you're in those lines of work. If not, one might have visited Schloss Hellenstein, the late-medieval castle which towers over the town.

Read more: Stuttgart and Hamburg: Bundesliga fallen giants' rocky road towards revival

But Heidenheim is also the setting for one of the most curious stories in German football, a story which has developed slowly, steadily but relentlessly over the past 26 years and which has taken 1. FC Heidenheim from the amateur leagues to the brink of the Bundesliga.

"It's simply surreal," said chief executive Holger Sanwald after Heidenheim booked their place in this season's Bundesliga promotion/relegation playoff, capitalizing on Hamburg's latest implosion despite their own 0-3 defeat to Arminia Bielefeld. "Sometimes, we have to run our eyes. But we know how to keep our development in perspective, and we're happy about that."

Sanwald knows exactly where Heidenheim have come from because he's been there every step of the way. The 52-year-old once played for the club but took over as chief executive at the age of just 27, gradually leading the club up through the leagues with patience, hard work and a broad network of medium-sized partners from the region.

"There's no room for one-man-shows here. We've worked our way up to our current situation over the years," said Sanwald. "There were always ups and downs but we always believed that we could continue."

Climbing up the leagues

In 10 years between 2004 and 2014, Heidenheim progressed from the fifth-tier Oberliga to the second division, where they have since plateaued — although there have been special highlights in the cup. In 2016, they were beaten 2-3 by Hertha Berlin in the quarterfinal. In 2018, they lost to Eintracht Frankurt. Last season, they pushed Bayern Munich all the way in a 5-4 thriller at the Allianz Arena.

"We're not a little village club,” insisted Sanwald in a recent interview with the Stuttgarter Nachrichten. "We have a budget of €35 million, which puts us in the top half of the division. We don't need to make ourselves any smaller than we are."

Directly responsible for Heidenheim's sporting ascent up the leagues is Frank Schmidt, who has overseen an incredible 467 games in his 13 years in charge, making him the longest-serving head coach in professional German football. The 46-year-old was only supposed to take over a couple of games back in division five, but he's still there. "There is no coach better suited to our FCH than Frank Schmidt," says Sanwald.

Marc Schnatterer, Schmidt's right-hand man

Having played almost as many games as Schmidt has coached is captain Marc Schnatterer, the veteran right-winger who joined the club in the Regionalliga in 2008 and has since scored 122 goals in 426 games — including one against playoff opponents Werder Bremen in a cup match.

For Schnatterer, now 34, promotion to the Bundesliga would be the perfect ending for one of Germany football's most loyal professionals. When he finally hangs up his boots, he's likely to take on another role within the club. That's how it works in Heidenheim.

But first, there's an extraordinary season to finish, the most successful in the club's history despite the unprecedented circumstances.

Heidenheim's big chance

On the pitch, Heidenheim beat Hamburg twice and recorded the second best defense in the league as they finished third. Off it, the club put money from the sale of Robert Glatzel (€6 million to Cardiff City) towards the purchase of the Voith-Arena from the city council.

The small, multipurpose stadium holds just 15,000, the minimum capacity for a Bundesliga ground, and is sponsored by Voith, the local mechanics manufacturer whose engineers set up predecessor club VfB Heidenheim in 1910.

And it won't be Bremen's first visit there. In 2011, Heidenheim beat them 2-1 in the first round of the cup, although the northerners got their revenge in this season's competition, winning 4-1. But neither side has ever played in the promotion/relegation playoff.

Since the re-introduction of the format in 2009, only three second division sides have prevailed: Nuremberg, Fortuna Düsseldorf and Union Berlin. Perhaps Heidenheim can make it four. It would just be another quiet step on their slow, steady journey.