The picture that shows you what makes Bilbao tick cannot be found in the Guggenheim. For all its undeniable magnificence, the Frank Gehry-designed gallery that rises sleekly beside the Nervió*River does not contain the famous photo of the celebrations after Athletic Club, the city's football team, won the Spanish league and cup double in 1984 (without the help of the hand of God). To find that, you'll have to go to the bar or, more accurately, you'll have to end up in one of the many bars in the city that display this striking image on the wall.
It's hardly an onerous task. Anyone who visits Bilbao and wants to enjoy the magnificent pintxos (tapas) for which the Basques are renowned will find themselves on the inside of a few drinking holes. Those who do will be struck by just how many places have some image related to the local football club on display.
Incidentally, the reason the name is English is because football was brought to the city by British sailors and migrant workers, well before it arrived in much of the rest of Spain: Athletic were founded in 1898 (some four years before the despised Real Madrid).
Visiting earlier this year, I lost count of the different bits of Athletic paraphernalia on show in various bars: club crests, banners, team photos, cartoons with mysterious and, no doubt, amusing legends in Basque below. Perhaps most frequently, I saw that image of Athletic's last great season. It shows the team on a barge chugging down the river as supporters swell the banks and the bridges, waving banners and scarves in the club's colours of red and white. Yet more fans are crammed on to other boats, in the wake of La Gabarra del Athletic. This ship has taken on almost mythical status in the 25 years since the club, one of the giants of Spanish football, won a major trophy.
The best place to see the picture is not in a bar, but deep in the bowels of the club's stadium San Mamés ("The Cathedral" to locals), a short distance upstream from the Guggenheim.
Athletic offer daily tours around this arena, opened in 1913 and with a main stand that dates from the 1950s. I was struck by how English it seems: like Goodison Park, except red and white. Like Everton's home, the ground has known slightly better days. There's a charming threadbareness about San Mamés, which has no corporate boxes.
This is a real blue-collar stadium. However, Athletic are building a new San Mamés (which will hold 53,000 fans, as opposed to just under 40,000 at present) alongside the current one, which is expected to be opened in 2013.
The clock is ticking fast on one of world football's most loved arenas. For the moment, though, visitors can admire the Tanzanian stuffed Lion (the club's nickname is the Lions) in the director's bar, the bust of Pichichi, the club's greatest legend, which faces the pitch yards away and at which opposing captains place flowers in tribute before every match, and the tiny dressing rooms: the home side's shower room looks as if it can accommodate, at a pinch, two footballers.
Then there's the press room, which is much larger – understandably given the rather greater dimensions of football journalists. Here you'll find the enormous picture of Athletic's last great moment.
A recent addition to San Mamés is the Exhibition Centre, a long, wide hallway stuffed with trophies and shirts. It gives you a real taste of what a key role this club has played in the history of Spanish football: Athletic have won the Copa del Rey (equivalent to the FA Cup) 24 times, while the title has come back to Bilbao on eight occasions. Four were in the first 10 years that the competition existed, from 1929, making the club Spain's first football greats. You can watch a film, too, of the 1984 celebrations: of that boat, of course, but also of the players' trips around the Basque towns where the passion for Athletic burns as it does in Bilbao.
There has been very little to celebrate in the past quarter century, but that loyalty remains unbroken. Last season the club qualified for the final of the Spanish Cup, held in Valencia in a stadium that can accommodate 55,000 fans. That didn't stop more than 100,000 Athletic supporters travelling and dominating the crowd.
Their side went down a 4-1 defeat at the hands of a remarkable Barcelona team, who also put paid to Manchester United's European Cup hopes.
To get a taste of this passion for the club, see a match at San Mamés. This place also sounds like an old-fashioned Football League ground: it's one of only four or five stadiums in Spain that generates a good atmosphere (in comparison with Real Madrid's Bernabéu or Barcelona's Camp Nou, which can make a day at the county cricket seem uncomfortably raucous).
The best time to experience this is when Real Madrid are in town and the locals get a chance to pour their bile on Spain's most-despised club. Basques have as much reason as anyone to hate Real, given the Madrid club's reputation (rightly or wrongly) as Franco's team.
In terms of loyalty, Bilbao is like a supercharged Newcastle, without the large-breasted men sporting Alan Shearer tattoos (there's also the difference in quality of pre-match food, of course). Not even Newcastle (renowned for producing many of England's best players), though, can match Athletic's commitment to local talent. The Bilbao side refuse to pick anyone who is not a Basque. This shows admirable restraint, but also explains why trophies have been thin on the ground lately.
It's an informal, unwritten policy that is constantly being debated: it may not survive should Athletic be relegated from the top flight for the first time in their history, as has seemed possible in recent years. What is certain, though, is that San Mamés is on borrowed time. Those wanting a taste of one of European football's most unique atmospheres need to move fast.
Travel essentials: Bilbao
*P&O Ferries (08716 645 645; poferries.com) sails every three days between Portsmouth and the port of Santurtzi, 14km downriver from the centre of Bilbao.
*Athletic Club Bilbao Museum, San Mamés Stadium gates 26-27, Calle Rafael Moreno Pichichi, Bilbao (00 34 94 441 39 54; athletic-club.net). From Nov-Feb the museum opens Tues-Sun 10am-2pm, and 4-6.30pm (closed Sun and match days); Mar-Oct it opens until 7pm. Tours on the same days 10.30am-6pm. Admission €6. Match tickets from BBK bank ATMs in the city. *Guggenheim Bilbao, Avenida Abandoibarra 2 (00 34 94 435 90 00; guggenheim-bilbao.es). Tues-Sun, 10am-8pm (and Mondays in July-August); €11.
*00 34 94 479 5760; bilbao.net.