9 km Under Hagia Sophia: What Istanbul’s Hidden Tunnels Mean for Tourism

Beneath one of the most visited monuments on Earth lies a network of tunnels nearly 9 kilometres long, and for the first time in modern history it is being cleared, mapped and reinforced. Türkiye’s Culture and Tourism Minister Mehmet Nuri Ersoy said on 3 November 2026 that about 3,000 tons of mud and debris have already been removed from the passages under Hagia Sophia in Istanbul, while engineers have begun reinforcing the main dome and the eastern semi-dome above. The minister calls it the most comprehensive restoration of the building in the history of the Turkish Republic. For tour operators, hotels, cultural sponsors and event organisers, the project is worth watching closely: if safe sections open to visitors, Istanbul gains a new underground attraction in the heart of Sultanahmet.

In brief

• Almost 9 km of tunnels: historic passages, water channels and underground chambers are being uncovered beneath Hagia Sophia.
• 3,000 tons removed: crews have cleared about 3,000 tons of mud and debris so far.
• Dome work has started: reinforcement of the main dome and the eastern semi-dome, where the mihrab and minbar stand, is under way.
• Exterior target: the ministry aims to finish most exterior work and remove most scaffolding by the end of 2027.
• Tourism stakes: Istanbul received 18.97 million foreign visitors in 2025, about 36% of Türkiye’s total.

What exactly is hidden under Hagia Sophia?

A system of historic tunnels, water channels and underground rooms that, according to the ministry, stretches to nearly 9 kilometres in some sections.

Minister Ersoy, speaking to reporters during the Antalya Culture Route Festival on 3 November, said the underground structures show how Istanbul managed water for centuries, with systems for rainwater drainage and water distribution. Some sections are high enough for a person to walk through, and in several places teams have found additional spaces that were not known before. In the minister’s words, the underground world is “at least as fascinating as the structure above ground”.

Work in the gardens around the building is already well advanced. According to a site inspection reported in August 2026, nine tunnel structures were identified in the West Garden, and fill soil was removed from all of them except Tunnels 2 and 8. A 56-metre underground space (Space-2) has had 18 metres of damaged vaults repaired with materials matching the original. Tunnel-4 received 50 metres of stainless steel reinforcement, and reinforcement of 90 metres in Tunnel-5 is in progress.

Why is this called the biggest restoration in Republic history?

Because it covers the entire monument at once: underground spaces, domes, minarets, mosaics, marble and the Ottoman tombs in the garden.

The project is run by the Ministry of Culture and Tourism under the guidance of a scientific committee, the regional conservation board and universities. Members of the scientific committee describe it as one of the most extensive interventions since the era of the great Ottoman architect Mimar Sinan, who added buttresses and minarets to the building in the 16th century. The full scope listed by the ministry includes the main dome, half and quarter domes, the Fatih and Mimar Sinan minarets, marble, plaster, calligraphy, mosaics, woodwork, the baptistery, the ablution fountain and the tombs in the south garden.

The plan is divided into four stages. By late August 2026 three were reported complete:

• Stage 1: restoration of the tombs of Sultans Mehmed III, Selim II and Murad III and the Princes’ Tomb in the south garden, including new lead roofing.
• Stage 2 (ongoing): earthquake strengthening of the minarets, work on the domes and mosaics. The northeast minaret was partly dismantled in a controlled way and fitted with stainless steel plates and rods.
• Stage 3: a new visitor route on the gallery level with ramps, a temporary entrance tunnel, ticket booths, X-ray and turnstile systems, new lighting, cameras and internet infrastructure.

Will the mosque stay open during the works?

Yes. The building remains open to worshippers and visitors while restoration continues.

To make this possible, a steel platform resting on the four main columns has been installed inside, so that prayers can continue beneath it while specialists work on the mosaics above. Because the inside of the dome is covered in mosaics, the main dome and semi-domes are being strengthened from the outside: the lead covering has to be removed and the main dome is protected by a temporary roof. Cracks had let water seep in and damage interior decoration. Once the dome is opened in a controlled way, radar and laser scanning will map hidden cracks. The ministry expects the main dome work alone to take at least a year of intensive effort.

When could visitors walk through the tunnels?

No date has been announced, but the minister has said that safe and suitable sections may open to visitors after restoration.

In September 2026 Ersoy said parts of the underground network are blocked by collapses and that mud and humidity are being removed or brought under control. The ministry’s target is to finish most exterior work and remove most of the scaffolding by the end of 2027, with work continuing in lower and hidden sections after that. Any underground route would therefore come later and would depend on safety assessments.

Why does this matter for Istanbul’s tourism economy?

Hagia Sophia is the anchor of the Sultanahmet visitor district, and any new attraction there adds time, and spending, to a visitor’s stay.

The monument receives around 3.5 million visitors a year. Since January 2024 foreign visitors pay an entrance fee of €25 and use a separate route to the upper gallery, while Turkish worshippers enter the prayer hall free of charge. The site sits next to the Hippodrome and the Basilica Cistern, part of the Historic Areas of Istanbul, which entered UNESCO’s World Heritage List in 1985.

The Basilica Cistern next door shows what an underground experience can do: it has become one of the city’s most photographed and best-selling attractions. A walkable section of Hagia Sophia’s water tunnels would create a natural pairing, a single “underground Istanbul” story told across two monuments a few hundred metres apart. The project also fits the ministry’s wider push on heritage in Istanbul: in October, five new museums opened at Topkapı Palace, which TRBW Creative covered in our report on the new museum quarter.

Who can benefit, and how?

Our take: the restoration is a long-term project, but several groups can start planning now.

• Tour operators and DMCs. Build flexible Sultanahmet itineraries. Scaffolding and closed areas will remain part of the view until at least 2027, so manage client expectations and highlight the restoration itself as a “once in a century” story.
• Hotels in the historic peninsula. Restoration news and underground discoveries are strong content for direct-booking campaigns, especially for culture travellers who return to Istanbul.
• Cultural sponsors and brands. Large heritage projects create demand for documentation, digital twins, exhibitions and educational content. Technology, engineering and insurance companies have a natural reason to associate with preservation work.
• Creative and media companies. Documentaries, VR experiences and photo books about the hidden tunnels can find international buyers, subject to permissions from the ministry.
• Event organisers. Timing matters: the ministry’s Culture Route festivals keep heritage in the news, and a future opening of the tunnels would be a major media moment for Istanbul.

FAQ

How long are the tunnels under Hagia Sophia?

According to the Ministry of Culture and Tourism, the network of tunnels and passages reaches nearly 9 kilometres in some sections.

Who is carrying out the restoration?

Türkiye’s Ministry of Culture and Tourism, guided by a scientific committee, the conservation board and universities.

Is Hagia Sophia open during the restoration?

Yes. It remains open to worshippers and visitors; a steel platform inside allows prayers to continue during the work.

Can tourists visit the tunnels?

Not yet. The minister has said safe and suitable sections may open to visitors after restoration, but no date has been given.

When will the restoration be finished?

The ministry aims to complete most exterior work by the end of 2027. The main dome alone is expected to need at least a year of intensive work, and work will continue in hidden areas after that.

How much does it cost to visit Hagia Sophia?

Foreign visitors have paid €25 since January 2024. Prices can change, so check official channels before travelling.

Sources

• Daily Sabah, “Hidden world beneath Istanbul’s Hagia Sophia emerges in restoration”, 3 November 2026: dailysabah.com
• NTV, minister’s inspection of the restoration, 28 August 2026: ntv.com.tr
• Habertürk, “Ayasofya’nın altında 9 kilometrelik tarih”, 17 September 2026: haberturk.com
• Time Out, entrance fee for foreign visitors, January 2024: timeout.com
• Hürriyet Daily News, Türkiye’s 2025 tourism income (TÜİK data): hurriyetdailynews.com

This article is for information only. Timelines and visitor rules may change; check official announcements of Türkiye’s Ministry of Culture and Tourism before planning trips or events.