SIKHS built four doors to the Golden Temple at Amritsar, in north India, to welcome believers from all four corners of their earth. But in the five centuries since, few religions have followed that tolerant example. Hindus and Muslims fight fiercely over religious ruins in ancient Ayodhya. Christians have long wrangled among themselves, and with other faiths, over Jerusalem’s holy places.

Yet a recent trend is more promising. In the past decade at least 1,500 multifaith prayer rooms have appeared in Britain alone, estimates Andrew Crompton, professor of architecture at Liverpool University, in research to be published in the Journal of Architecture. At least 90 are open to the faithful (and often to the faithless too, represented by a blank space on multifaith signs) in airports, according to the International Association of Civil Aviation Chaplains. A prayer room in the Zurich railway station draws up to 1,000 visitors daily during Swiss holidays.

A few airport rooms are converted chapels, such as Our Lady of the Airways at Boston, originally built for Catholics in 1952. But most are built from scratch. London’s Heathrow airport now has ten, with two under construction. They can be found at football venues (from FIFA’s headquarters in Zurich to the Etihad Stadium in Melbourne), at shopping centres and some motorway service stations.

Secularists bristle. Terry Sanderson, president of Britain’s National Secular Society, says that Muslim prayer needs have fuelled the demand: multifaith rooms are, in effect, mosques that creep into the public space, cloaked behind political correctness. But they are also a product of public attitudes that are unconcerned about religious difference, suggests Johannes Stückelberger, a theologian and expert in church aesthetics at the University of Bern in Switzerland.

Designing a sacred space that can cater to all faiths is a headscratcher for architects. “No one yet knows how to do it,” says Mr Crompton. Some attempts to be scrupulously inclusive, by using Lazy-Susan altars (which rotate to face east for Catholics or to Mecca for Muslims, as required), may be offensive. Those that are too mechanised, such as the German Gebetomat—a vending booth for prayers in 65 languages which Mr Crompton dubs “multifaith for cheapskates”—can seem tacky. The preferred solution in many places has been to furnish rooms as neutrally as possible.

That need not mean banality, says Carol Phillips, who designed Toronto University’s multifaith prayer hall. To create a non-specific sense of ritual and reverence, she stressed light and nature. Onyx ceilings and walls filter the light. Ventilators remove the scent of burnt sweetgrass (a feature of native American gatherings) for subsequent users. A symbolic split entrance allows Muslim women to pray out of the view of men. Screened alcoves conceal Hindu deities.

Even the best-designed spaces need continual attention. Some ban proselytising. Prayer mats or temporary religious paraphernalia can become permanent fixtures. At Heathrow Devraj Singh Khalsa, the Sikh pastor (one in an interfaith team of 22 clerics) ended up trying to soothe Shia Muslims whose clay praying tablets were being binned by puritanical Wahhabi users, who follow Sunni Islam (the Muslim minister, a Sunni himself, says relations are harmonious). The chaplains’ call-out rota means they must help people from other creeds too. Mr Singh often reassures anxious Christians before they fly.

Frankfurt’s Goethe University is the first in Germany to have a multifaith Haus der Stille, or house of silence, which opened in 2010. Eugen Eckert, its Protestant chaplain, recalls a dispute between a female Christian student and a male Muslim scholar who asked her to pray elsewhere. Most take it in turns to use the room, rather than pray together. But Catholic and Muslim ministers hold a monthly peace prayer.

For Mr Crompton the real innovation is ministers working together on problems that arise from such unusual religious spaces, not “hideous” new architectural blueprints for them. The best designs are those that develop organically: impromptu, cheap and temporary. “Architecture often spoils the party,” he admits. Some of the most successful prayer rooms came about without professional advice, hastily squeezed between the toilets and the lifts. God is there too.