RTL Today - Hidden below Luxembourg's justice quarter: The 'Crypt of the Holy Spirit' to open for the first time in 2025

Hidden for decades beneath layers of sand, the archaeological crypt under Luxembourg City’s justice quarter is set to welcome visitors for the first time in spring 2025, with a permanent opening planned for 2026. This historic site promises to be a significant addition to the city’s UNESCO World Heritage treasures.

A hidden gem of the capital

Luxembourg City’s old quarters and fortifications have been celebrated as UNESCO World Heritage Sites for 30 years. Beneath the sprawling justice quarter, constructed on the Plateau du Saint-Esprit in the mid-2000s, lies the archaeological crypt – a site of immense historical importance. Once concealed under 3,000 tonnes of sand for preservation, this hidden treasure will finally emerge from obscurity to the public from Easter 2025 onwards.

"The site will temporarily open in 2025 during La Luga to celebrate 30 years of UNESCO designation," shared Eric Thill, Luxembourg’s Minister of Culture and Delegate for Tourism, with our colleagues from RTL Infos. "Its definitive opening is planned for 2026, fulfilling Luxembourg’s promise to UNESCO."

La Luga – short for “Luxembourg Urban Garden” – is an ephemeral exhibition spotlighting green spaces in Luxembourg City’s urban belt. Running from 7 May to 18 October 2025, this event will coincide with the crypt’s temporary opening, offering visitors a unique opportunity to explore the city’s hidden heritage.

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Free digital tour as of today

In a bid to make the city’s rich history more accessible, the Ministry of Culture has launched a digital tour of the Fort du Saint-Esprit. Starting today, anyone can embark on a virtual journey through the citadel’s underground labyrinths, once accessible only to specialists due to safety concerns.

Using an AI-powered headset, the 3D tour offers an immersive experience. Visitors can navigate 350 steps underground, explore hidden passageways, and examine historic artefacts. Interactive thumbnails provide detailed insights into the military and architectural significance of the fortifications, a cornerstone of Luxembourg’s medieval defence.

Explore the crypt by walking through virtually. / © Ministry of Culture, Matterport / Screenshot

What awaits visitors in the crypt?

The archaeological crypt spans over 1,000 m² and houses remnants of the Poor Clares convent, founded in 1234 by Countess Ermesinde. Though the convent was demolished in 1770, its foundations endured, with subsequent uses by military forces until 1966. Excavations by the National Institute of Archaeological Research, meticulously documented by the Museum of History and Art, reveal a narrative of resilience and transformation.

Visitors will encounter medieval convent structures, remnants of Vauban’s fortifications from 1685, and 19th- and 20th-century additions, including kitchens, stables, and laboratories. An intact secret door within the Holy Spirit Fortress wall offers a dramatic entrance to this historical treasure.

Walk through time

To preserve the integrity of the site, 220 metres of suspended walkways are being installed. These will provide visitors with a comprehensive view of the crypt’s structures while avoiding direct contact with the delicate remains.

Certain sections will widen to create educational zones with multimedia displays and rest areas, enriching the visitor experience. Lapidary elements uncovered during excavations will also be displayed, offering further insight into the architectural and cultural legacy of the convent and fortress.

The project, launched in 2022, is expected to be fully completed by 2027.