Beneath Cologne’s businesslike exterior is a quirky side that is ripe for exploring, says Andrew Eames

When it comes to city attractions, the “longest underground car park in Europe” doesn’t have all that much sex appeal.

But whether or not you are aware of its celebrated status, if you steer your hire car down into Cologne’s 1.6km-long Tiefgarage Rheinauhafen you will be in prime position to explore the city’s newest, snazziest business and leisure district, the Rheinauhafen, located directly above your head.

Situated on an island-peninsula, around a former commercial harbour on the River Rhine, this is Cologne’s equivalent of London’s Docklands, with an eclectic mix of design shops, chic restaurants and over-arching (literally, in the case of the three striking Kranhaus, or “crane tower”, buildings) modern architecture, along with those clever conversions of traditional warehousing that are characteristic of docklands all over Europe.

The area also hosts the city’s perennially popular Chocolate Museum (schokoladenmuseum.de; open Tues-Fri 10am-6pm, Sat-Sun 11am-7pm; entry €9), good for picking up gifts to take home.

Even if you’re not staying in the new and trendy Art’otel (artotels.com), which looks directly across the harbour to the Rheinauhafen, it is still worth coming here for a sunset cocktail on the terrace of the hotel’s Chino Latino restaurant.

A little further south is Limani (limanicologne.de), where you can tuck into meze and shellfish while watching the Rhine barges and cruisers slip past. Your neighbours on the terrace may be well-heeled Microsoft hipsters kicking back after a hard day at the coalface – one of the new buildings in the Rheinauhafen is the company’s regional HQ.

This adventurous urban development is the latest evolution of a city that is made for business. But, despite the first impressions that may be created from the huge railway station, adjacent soaring cathedral and pedestrianised hinterland, Cologne is far from being typically German.

This is, after all, the home of one of Germany’s biggest gay communities. It’s also home to the largest brothel in Europe, Pascha, with over 100 sex workers in a blue-painted 12-storey block in the suburbs.

It is the city that hosts several huge European trade fairs, yet so completely lets its hair down during Carnival (a week-long street festival that begins on the Thursday before Lent) that there’s no point in waiting for an answer to emails, let alone expect anyone to be remotely coherent on the phone.

In fact, Carnival is more than just a week-long celebration – it is one of the fundamental building blocks of Cologne society. Look inside a Kolner’s wardrobe and you’ll find he’s likely to have a secret life as a clown or a pirate, with a costume that could easily have cost him over €2,500, and signifies his association with one or other of the 160 Carnival societies.

These societies are not just once-a-year affairs but powerful and effective fundraisers, and, like workers’ unions, they organise holidays for those members who would otherwise be unable to afford them, and even look after them if they become sick.

Carnival is easily Cologne’s most eye-catching experience, distracting visitors from the otherwise insipid architecture of the downtown area (it was heavily bombed in the Second World War). To make up for it, there’s a true buzz on the streets and a sense of creativity in the air.

Take the hotel selection as an example – besides the Rheinauhafen Art’otel, there is also an upmarket business hotel secreted in a water tower (Hotel im Wasserturm, hotel-im-wasserturm.de), where much of the furniture is custom-made to fit the curved interior walls. Another is the Chelsea (hotel-chelsea.de), where artists used to be able to pay for their board with works of art.

Even the shopping centres come with a twist. Over in the WDR Arkaden (on the corner of Breitestrasse and Tunisstrasse), after browsing the quirky stores, you can gaze through soundproofed glass into the production studio of regional broadcaster WDR and watch TV shows being made.

Still, Cologne’s commercial strength isn’t just about recent development. The Romans were here, because of the strategic location of the river port, although much of what they built has been subsumed in all the modern post-war construction.

You can, however, walk through the remains of the Roman governor’s Praetorium and the sophisticated sewer system (open Tues-Sun 10am-5pm; entry €3.50) underneath the Rathaus (city hall). If you’re short on time, nip downstairs past the cake displays in Breitestrasse’s Café Fromme to admire the Roman remains emerging from the walls. You should probably buy a cake, too, if only to be polite.

While on the subject of eating and drinking, modern Cologne takes an unorthodox approach here as well. In this city, a Halber Hahn – half chicken – is actually completely fowl-free, being a bread roll with cheese.

Kolscher Kaviar, Cologne caviar, is not from sturgeon in the Rhine but is actually a dish made from blood sausage and onions. And Himmel und Aad – heaven and earth – may sound glorious but is in fact made from a mix of mashed potatoes and apples. Try them at Peters Brauhaus (peters-brauhaus.de) or Brauhaus Sion (brauhaussion.de).

While the rest of Germany serves its beer in huge one-litre steins, Cologne presents its chilled kolsch in straight 0.2-litre glasses, believing its beer is something to be sampled fresh from the keg.

One of the best places to sit for an impromptu drink of any variety is Brusseler Platz, in the arty Belgian quarter. In the evening, the square, dominated by the neo-Romanesque church of St Michael, becomes an al fresco bar, filling up with locals who buy their drinks at the kiosks, and sit and talk.

Ultimately, most international visitors will end up gravitating towards the river. On summer evenings there is a real Mediterranean feel to the Rhine promenade, which fills with families, rollerbladers and lovers, some of whom will have probably left love-padlocks up on the Hohenzollern bridge, the busiest railway bridge in Europe, and chucked the keys into the water as a symbol of their undying love.

Eventually, most people will end up in front of the huge Gothic Cologne Cathedral (koelner-dom.de), whose survival through the ravages of war is something of a miracle. Its blackened exterior, encrusted with sculptures and carvings, belies a surprisingly delicate interior. It is well worth spending the €3 to climb up the steeple (9am-6pm daily) for the view, and for the sheer immensity of all that ornamental stonemasonry – most of which would be otherwise only for the benefit of steeplejacks, pigeons and God.