Since then the former seminary has been a drugs rehabilitation centre, a place for illicit trysts and parties, and now – after discussions that have gone on for some years – a public arts centre. The ruins of St Peter’s are certainly artistic. It is easy to imagine them as a set for an unmade film by Andre Tarkovksy: the Russian director would have loved these religious spaces invaded by trees, by rain and mists, with pools of water on uncertain floors and ethereal sunlight piercing glassless windows.

Restoration drama

No one is likely to restore St Peter’s to the condition it was in its brief heyday. Not only would this be inordinately challenging and expensive, but also no one –least of all the Catholic Church – wants a 1960s concrete seminary here. Although artists may colonise it, St Peter’s future may well be that of a ruin, shored up to be safe, but no more or less than that.

In 1987 I visited the House of the Communist Party of Bulgaria on a trip organised by the Union of International Architects. The Union’s president was Georgi Stoilov, the former communist guerrilla who fought the Nazis, former mayor of Sofia and acclaimed architect. The House had opened in 1980. Situated on the top of Mount Buzludzha in the heart of a sweeping national park, this extraordinarily remote building came as complete surprise. It takes the form of a huge upturned concrete bowl, or flying saucer, accompanied by a splayed 107m (351 ft) tower. Commanding the landscape where Bulgarian rebels fought hard against the Ottomans in the late 19th Century, this was a monument to nationalist as well as Communist Party sentiments.

Behind its imposing facade adorned with communist slogans carved into the concrete – “On your feet, despised comrades/On your feet, you slaves of labour’ – was a colossal, top-lit domed chamber surrounded by colourful murals depicting communist heroes. A very long way from Sofia – a long way from anywhere – it was not exactly surprising that when Bulgaria’s communist regime fell in 1989, the building lost both its purpose and its soul.

Today, it is a ruin, its great glazed roof open to the elements. Some want it demolished, others saved as a historical monument that might double up as a profitable tourist attraction. Its fate, though, may well be as a ruin for although haunting, it is just one of many bravura communist monuments many more people prefer to forget.

Other despised regimes produced even more ambitious 20th Century monuments than Bulgaria’s Communist Party. What to do with their concrete carcasses and stone shells? The broken ruins of Hitler’s terrifying forward command centre – Wolfsschanze in the Masurian woods in north-east Poland – lurk between trees, half-hidden by climbing plants. This is where Colonel Claus von Stauffenberg and his fellow conspirators failed to assassinate their Führer in July 1944. Wolfsschanze is a sinister place even if its concrete buildings look similar to the Brutalist architecture of the 1960s, fashionable again today, found in so many French and British cities. And, yet it is of great historic importance and for this reason alone will probably be left for future generations to ponder.