Listen to Huw's chat with Rhidian, the site warden.

Details for visiting the reserve.

Seventeen million grenades and other munitions were made at Cooke's Explosives Ltd during WWII. Nowadays it's an extensive nature reserve where the most lethal thing is an adder.

The site has a long history of explosives production, starting from 1865 with gun cotton, then TNT and a range of safety explosives for the mining industry. With the demise of British coal mining, the business was no longer economically viable and closed in 1995.

Three years and £6m of decommissioning later, the site was donated by ICI to the North Wales Wildlife Trust.

It's a brilliant place to explore, bringing together a mix of natural and industrial history. It used to be the biggest employer in the area with a workforce of 500 in the 1960s, but today's only employee is Rhidian, the warden, helped by a small army of volunteers.

A massive explosion in 1915 (perhaps enemy sabotage) destroyed the facilities, and responsibility for the site was taken over by the Ministry of Munitions before being sold to Cooke's in the 1920s.

A key feature of the 200-acre site is the partitioning into three valleys. In the wake of the big accident, production was distributed across the valleys to limit the risk of an explosion in one area spreading to the other.

One of these was called Klondyke Valley because the pipework required for producing nitro-glycerine resembled a gold-rush town.

The plumbing has gone, but one of the key buildings remains; the settling shed. Amongst other things this housed seven settling tanks in which residues of nitro-glycerine were removed from the water used to keep the explosives cool and stable.

When explosives are being mixed it's essential to keep them cool and the process involved piping in water from a nearby pond with an operator monitoring temperature and flow. This worker was provided with a stool, but for his protection it had just one leg. If he fell asleep, it would not be for long!

This is the most modern of the buildings, dating back to 1988 when a huge blast destroyed the previous one, killing two of the employees and shaking buildings in Penrhyndeudraeth like an earthquake. Today it's an education room for visiting schoolchildren and a bird hide with wonderful views onto the estuary below and heathland beyond.

As for the pond from which the water was piped, Rhidian treated us to the delights of pond dipping, scooping out dragonfly and damselfly larvae, water boatmen, palmate newts and mating toads - necklaces of toadpoles everywhere.