A visit today (in appalling weather) to the former RAF Bomb Store in Llanberis.
In 1939, The Air Ministry took over the former Slate Quarry at Glyn Rhonwy for use as an Ammunition Store. They built a two storey concrete building within the former quarry and piled 40 feet of slate waste on top to disguise it. Unfortunately, a poor design meant that a large section of the building collapsed, burying thousands of tonnes of ammunition and an entire train. As 20% of the entire RAF ammunition supply was stored here, this was a major calamity. The collapsed section was cleared but not rebuilt. The site continued in use until the 1950s. Then it was discovered that hundreds of tonnes of faulty explosives etc had been simply dumped in the lakes by the sides of the quarry. This resulted in a major clean up operation which lasted until 1976. The site is now awaiting development.