Manod Quarry

Overview

A slate quarry east of Blaenau Ffestiniog, known formally as Bwlch y Slaters (and also as New Manod or Graig Ddu), that secretly housed the National Gallery's entire collection -- including works by Rembrandt, Velazquez and Leonardo da Vinci -- through the Second World War.

History

Quarrying at the site began in the 1780s as open workings, with significant underground development following a tramway connection made in 1866; a second working opened in 1903. Following the fall of France in 1940, government surveyor Francis Rawlins inspected the quarry in September 1940 and identified five disused chambers suitable for secure, climate-stable art storage. Brick-built enclosures with environmental controls were built inside the caverns, and by summer 1941 the entire National Gallery collection had been moved there from Wales's earlier, more dispersed wartime storage sites; the paintings returned to London in 1945. The quarry itself has since been distinct from the modern working two miles away that adopted the name 'Cwt y Bugail' after that older quarry's own closure -- a naming overlap already noted on MineArchive's own Cwt-y-Bugail Quarry record.

Closure

Slate production was suspended in 1960 and resumed after 1985 with new milling equipment.

What remains

Managed as an active slate working in places and not open to the public; wartime infrastructure has mostly been removed, though the chambers used to store the paintings survive. The National Slate Museum at Llanberis holds an interpretive display on the site's wartime history, and the National Gallery itself unveiled an inscribed slate tablet in 2024-25 commemorating the quarry.

Abandoned workings can be dangerous — unstable ground, uncapped shafts, flooding and bad air are common even where a site looks safe from the surface. This entry describes history and general location only; it is not an access guide.

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• Quarrying at the site began in the 1780s as open workings; significant underground development followed a tramway connection in 1866, and a second working opened in 1903. ¹
• Francis Rawlins surveyed the quarry in September 1940 and identified five disused chambers suitable for art storage; brick enclosures with environmental controls were built inside, and by summer 1941 the entire National Gallery collection, including works by Rembrandt, Velazquez and Leonardo da Vinci, was housed there until returning to London in 1945. ^1,2
• Production was suspended in 1960 and resumed after 1985 with new milling equipment. ¹
• Alfred McAlpine operated the quarry, by then locally known as Cwt y Bugail, until ceasing operations there in late 2007. ³

Photographs & further reading

This page doesn't try to reproduce everything — these are the best original sources found for this mine.

Sources

1. (secondary) Bwlch y Slaters quarry — Wikipedia
2. (secondary) Manod Slate Quarry (Chwarel Manod) — Subterranea Britannica
3. (secondary) Bwlch y Slaters Quarry — Festipedia

Record created: 29 August 2026 · Last researched: 29 August 2026