THERE can’t be many cities in the world that would allow you to walk by one of its architectural masterpieces without any fanfare, but that’s exactly what happens day in, day out, on Glasgow’s Garscube Road.

Charles Rennie Mackintosh’s church sits quietly, unobtrusively, on this busy urban intersection in Queens Cross, the working class district between Woodside and Maryhill, just north west of the city centre. Cars whizz by and pedestrians pass without a second glance. On the day I visit heavy rain is pummelling everything in sight, and the elegant red sandstone exterior looks almost black in the fading light.

Those who do take the time to go inside, however, are in for a real treat, as this extraordinary building offers visitors not only an astonishing feast of artistic endeavour but also - if you let it - a spiritual dimension, too.

With this in mind, the church provides the perfect headquarters for the Charles Rennie Mackintosh Society, the independent, non-profit charity that has been celebrating, preserving and promoting the work and legacy of the Glasgow-born architect and designer since 1973. The Society took over the building in 1977, when it was abandoned as a place of worship, and has cared for it ever since, raising more than £1m in 2007 for the major restoration that now showcases the unique and enduring beauty of Mackintosh’s only church.

Aficionados have long held this place in high esteem – Princess Margaret came for a private visit in the 1970s and apparently played the organ - but in comparison to some of Mackintosh’s other buildings, such as Glasgow School of Art and Hill House, it remains under the radar.

“People sometimes don’t go exploring in their own city,” says the Society’s director, Stuart Robertson, who has run the organisation for the last 16 years, as he takes me round. “This church is still something of a hidden gem in Glasgow. Over the last few years we’ve opened it up for concerts during the Celtic Connections festival and many people who come are blown away by it. They can’t believe how beautiful it is.

“Sometimes when I’m here on my own I can really feel the soul of this building. It’s a truly special place where you can meditate upon life, an oasis of calm in the middle of Maryhill - just as Mackintosh intended.”

As you explore this building, which was originally commissioned by the Free Church of Scotland in 1896 and opened a year later, you can understand why Mr Robertson and others might respond to it in such a way. Unlike some other churches of the late Victorian period, there is nothing overblown or austere about this place, either inside or out. Indeed, if anything, there is a warm and sensuous feel.

Though Mackintosh was still a trainee architect at Honeyman and Keppie when he designed the church – it was completed before his 30th birthday - the full artistic vision he became celebrated for in his later masterworks, such as Glasgow School of Art and Hill House, is already in evidence here.

The elegant natural forms and motifs that Mackintosh would become renowned for can be seen throughout the church, at the ends of the pews and in the pulpit, in the ceilings and on the stonework. There’s a cheeky sense of humour at work here too, as images of the birds and the bees decorate what would have been a place of strict Presbyterian worship. The stained glass is particularly beautiful, its purples and greens vibrant and visceral, lighting up the space on even a dark and gloomy autumn day. Beside the pulpit sit two original chairs that would not look out of place in a contemporary home thanks to the clean lines and graceful simplicity.

According to Mr Robertson, a formal naval architect, it is this sense of timeless modernity that still attracts people to “Toshie”, as he was known to close friends.

“Mackintosh was ahead of his time,” he explains. “He was feted across Europe and the US in his lifetime but not here in the UK. When the Society took over this church, few were interested in his work.

“Many more people appreciate Mackintosh now, of course. But the legacy is fragile, and it should be noted that we receive no public money.”

Next year – the 150th since Mackintosh’s birth - is a big one for both the Society and the aforementioned legacy, and there are exciting plans in the pipeline for a wide array of celebrations and events.

This is a particularly interesting and exciting time for Mackintosh’s legacy, of course, what with the £35m restoration of the fire-damaged Mackintosh building at Glasgow School of Art and the £10m redevelopment of the Willow Tea rooms in Sauchiehall Street, both well underway. There are also plans to redevelop both Hill House, in Helensburgh, and the Mackintosh House at Glasgow University. Meantime, next month plays host to the annual Charles Rennie Mackintosh Festival, run by Society, which features tours, workshops, music events, puppet shows, and, this year, the chance to view unseen works by the artist.

Around 40 volunteers help keep the Society running, and with so much ongoing activity, Mr Robertson hopes to recruit 20 more in the coming months.

“We’re working with the city to make Mackintosh a more prominent element of the tourist plan,” he adds. “What drives all of us at the Society is the enthusiasm of the visitors we meet, the love and affection they have for Mackintosh’s work.

“His legacy wraps into the contemporary world so easily - he continues to inspire people.”

The Charles Rennie Mackintosh Festival runs throughout October at various locations. For more information go to www.crmsociety.com