Beyond the E871 highway and after the last premises of Sofia's Business Park, a white metal palisade shields an immense building site. The borehole drilling resonates from within. The summer sun is burning. With Vitosha mountain against a clear blue sky for a background, a sandy country lane meanders up a plateau.

Colourful weeds grow tall on both sides of the lane. Modest houses in peeling orange, green or yellow hide behind the old trees. Above them, towers a massive concrete structure, rising from the plateau: Kambanite, or The Bells.

The site, a leafy park of 25 acres, breathes serenity. Despite the nearby road, the place is remarkably quiet. A fountain sprays cold water. It appears that I am the only visitor.

Few people realise that The Bells are Europe's largest percussion instrument

The Kambanite monument was built in 1979, in just 30 days. Back then, it was called Banner of Peace Monument and was part of the activities for the first edition of the Banner of Peace International Children's Assembly. The assembly was an arts festival designed to establish Bulgaria's prestige abroad. It was a joint initiative of UNESCO and Bulgaria's Communist regime, in particular its de facto Minister of Culture Lyudmila Zhivkova, the daughter of dictator Todor Zhivkov.  UNESCO's then-director general, Senegalese Amadou-Mahtar M'Bow, praised the assembly as "an opportunity for many children, brought up in various cultures, to understand that despite their differences a universal language of brotherhood and solidarity exists – a guarantee and hope for the future."

Children of 79 countries participated in the founding event. By 1989, when the event was discontinued in the wake of Communism's collapse, there were five more editions, and more countries had joined the festival. Ringing the bells at the Banner of Peace monument was an integral part of the festival's programme.

Relief of Lyudmila Zhivkova, surrounded by the children of the world

The monument was designed by architects, Blagoy Atanasov and Gancho Ganchev. Every detail in the structure was meant to symbolise the universal reach of the philosophy behind the monument. A 37-metre-high tower of four pairs of concrete pillars rises in the centre of the structure. Each pillar represents a cardinal direction. The open sphere at the tower's top has seven bells – a symbol of the globe and the seven continents. A circle of 186 pedestals, most of them holding a bell, surrounds the tower. Every bell was donated by a different country. Some of these no longer exist: Yugoslavia, Czechoslovakia, the DDR. The bells' sizes differ, and so do their designs. Bulgaria's massive bell, for instance, weighs 1.3 tons, referring to the fact that the country was created 1,300 years ago.

A sculpture of Lyudmila Zhivkova, surrounded by children from all over the world – a favourite topic of 1980s public art in Communist Bulgaria – stands at the bottom of the monument. It was made by the renowned artist, Krum Damyanov.

The botanical garden around the monument features exotic species: each country delegation donated not just a bell, but also a specimen of local flora.

The monument carries a bilingual motto: "Unity, creativity, beauty." It was a favourite slogan of Zhivkova, a sign of the strong influence of Russian artist and esotericist Nicholas Roerich's ideas on her.

The Banner of Peace Assembly was discontinued when the Communist regime in Bulgaria collapsed, in late 1989. In April 1990, the Banner of Peace monument was renamed The Bells. It was abandoned, and in the 1990s, a time of economic uncertainty and widespread unemployment, some of its bells were stolen for scrap metal. In 1996, the monument was even threatened with demolition.

Evgeniya Zhivkova, daughter of Lyudmila and a politician, tried to restore the Assembly, in 1999. For the next 20 years, her foundation organised children's concerts and exhibitions as a scaled-down replica of the 1980s events.

In the 2000s, the monument continued to attract the attention of sometimes rather surprising organisations and players. New bells were hung – from the Vatican, NATO, the Rotary Club and even from some private companies.

Inevitably, the area grabbed the attention of luxury property developers, too. The Bells and its park are in one of the most appealing areas around Sofia – close to the Vitosha and its nature, with relatively easy access to the city. By the early 2010s, luxury developments, gated communities and business facilities had sprung around the monument, engulfing it and replacing older houses with their manicured gardens, barriers, security guards and CCTVs.  

Fun facts about The Bells

• One of the bells was made in the 9th century.
• A bell from Latin America was used in a... revolt.
• Along with The Bells in Sofia a "children's railway" was constructed in Plovdiv. It is still in existence.
• The Bulgarian bell weighs 1,300 kg in celebration of the 1,300th anniversary of Bulgaria's foundation.
• The Bells was slated for demolition in 1996.
• Kambanite is the largest percussion instrument in Europe.

The old sign to the monument has survived since the early 1980s