“The first thing I’m going to ask is can you just watch your step, please?”

My tour guide for the morning points out the various wooden trip hazards that run along the middle of the corridor, doing a makeshift job of covering up pipe holes.

I’m standing 50 metres below ground level at Dover Castle – though given how high the cliff is, I’m still quite high up in comparison to sea level – where the “secret” Dumpy tunnels are situated.

The heads-up from the guide is one of many signs that this long-neglected cave-like system of rooms needs some fresh life injected into it.

Paint peels from the walls and ceilings. The metal which lines the roof of the tunnels – from Pennsylvania, USA, thanks to the British metal shortage of the Second World War – is rusting and around me. There’s an eerie air of what could have been.

Constructed in 1942 by the Royal Engineers, Dumpy is the youngest of the wartime tunnels at the castle – and is by far the least explored.

Part of that is due to its lack of accessibility – there is just one lift that goes down to the area and the emergency escape route is an 80-step staircase.

Another part of it is due to the severe health risks Dumpy presented when English Heritage first looked to open all the tunnels – which it did in the early 1990s.

I can almost hear the hustle and bustle of the busy voices of years gone by before remembering the tunnels have spent the vast majority of their life waiting in anticipation of what comes next.

My footsteps echo through the labyrinth of corridors and side rooms, a grave reminder of how isolated you are down here.

There’s no sunlight, no outside noise, no phone signal – not that I’d want to be scrolling through social media during a fascinating trip to a whole new world.

A world which demands you hear your breath and listen to your heartbeat as well as the rattling of the vents – a world now so devoid of life except your own.

That said, one construction worker in the tunnel with us can recall a time when the walls dripped and the mould was so thick anyone spending time down there needed to wear full-body suits – so it wasn’t always just a concrete void.

Of course, things aren’t quite like that anymore – thanks to the fine work of dehumidifiers – and, if anything, the air down here feels cleaner than outside at the docks thanks to the ventilation systems in place.

But tours of the long-abandoned Dumpy level are a rarity and, even now, the staff still get excited at the prospect of being sent down the tunnels to carry out maintenance work or just to have a look around.

The tunnels have a fascinating backstory, one which deserves to be shared but often gets forgotten about in the grand scheme of things thanks to the crucial role the castle’s other tunnels played in helping Britain defeat the Nazis.

Dumpy’s roots may come from the second half of the war, but its later purpose was in the Cold War, the period of modern history which saw tensions linger between the Soviet Union and the Western world.

In the early 1960s, the Conservative government selected Dover Castle to be one of 12 regional seats of administration, only to be occupied in the event of nuclear war.

Should the worst happen, a senior minister was to be in charge aided by military and civilian staff with the task of creating some form of administration after a nuclear attack.

With chalk being a porous material, meaning it would soak radiation up like a sponge, Dumpy’s depth into the cliffs was considered to be one of its finest attributes as opposed to the other tunnels, Casemate and Annexe.

All three would play a part – with Annexe refitted as accommodation and the western tunnels of Casemate also repurposed to make dormitories, dining and catering areas and restrooms.

Rooms in the Dumpy tier were reconfigured from their wartime purposes to keep in mind the demands and services the public would need, such as unemployment and pensions, police, transport and agriculture.

Even the BBC was poised to have a presence in the tunnels, with a studio set up to broadcast to the workers – though initial hopes of playing relaxing music 24 hours a day were shelved as the limitations of finite battery power became clear.

So, had another scenario played out, one which saw nuclear war break out in Europe and the USA, Dumpy would have become the heart of the regional government.

And being in such close proximity to London – which was the most likely target of any bombs – Dover very well could have been the new home for the top dogs.

Unlike the radiation which would have beamed itself onto anyone down here if the unthinkable had happened, there’s not much love radiating from the walls – it’s very matter-of-fact and cold.

I don’t feel as though this would have been a happy place to work or that people would have been able to make a good go of even trying to force out a smile down here.

For a war that came and went without a single bullet, let alone a nuclear bomb, the Cold War has imprinted itself in the atmosphere of the tunnels so much that 60 years later, it’s slightly uncomfortable to remember what this was all for.

Luckily for me, this bygone era disappeared long before I appeared and even if it hadn’t, I would have provided nothing worth hauling me down here for – only the best civil servants and top-skilled workers were considered by the government.

But those being eyed up for possible relocation to Dumpy were often unaware their names even featured on such a list.

Potentially being sent down a month at a time, workers would have been asked to bring a change of clothes and a book.

With storage space being limited – and as a symptom of being buried in the middle of the ground – only two gallons of water a day would be available per person for all purposes.

A certain generation of Dover residents share tales of breaking into Dumpy when they were youngsters and finding a whole world of relics wasting away – including fire extinguishers and switchboards which still linger in the halls to this day.

Some even recall finding weapons stored in some of the side rooms of the tunnels – though whether or not there is any truth to this is beyond the knowledge of anyone at the castle nowadays.

Work continued to take place in Dumpy up until the 1980s – with a new toilet block being installed at some point in the late 1970s – before the tunnels were decommissioned.

Having glanced a peek at the toilets, you wouldn’t guess they’re that old – you could count on one hand the number of people who made use of them.

Because Dumpy’s time to shine thankfully never came around, condemning it to fall into disrepair before works lasting as long as 20 years saw it finally become somewhat fit and proper to host people again.

By all admissions, there is still work to be done, with the space naturally being very restrictive – the number of people in the tunnels has to be carefully monitored so as not to overload them.

Tours are expected to last until the end of January, though this could be extended or shortened depending on how demand plays out.

Tickets to the tour can be bought on the day on a first-come-first-served basis and will be an additional £10 on top of the entry to the castle – with no under-18s being allowed for safety reasons.