Inside Adolf Hitler's secret underground tunnels 'where Nazis tested new weapons in the final days of World War II'

These remarkable pictures lift the lid on long-abandoned German tunnels that are believed to have led to a secret Nazi weapons testing bunker.

After hunting through miles of underground passageways, urban explorer Warren Tepper, from Hampshire, was shocked by his discovery after climbing through a hole in one of the reinforced concrete walls.

It is claimed the area was a World War II shelter for Nazis during the bombing from Allied forces and also a bombardment system, where ammunition was tested on steel plates.

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PICS BY WARREN URBEX / CATERS NEWS - (PICTURED: Smattered with bullets, this is the control room where it is believed allied forces raided the location - bullets still are lodged in the bullet proof glass several inches thick) - An urban explorer has revealed abandoned German tunnels claimed to lead to a secret Nazi weapons testing bunker. After hunting through miles of underground passageways, Warren Tepper, from Hampshire, was shocked by his discovery after climbing through a hole in one of the walls. It is claimed the area was a shelter for Nazis during the bombing from Allied forces and also a bombardment system, where ammunition was tested on steel plates. Inside Warren and co-explorer Matt, found four-inch-thick bullet holes in metal along with similar holes in bulletproof glass, believed to have been from when Americans raided the site. The bunker and surrounding tunnels, that lie beneath Duisburg, Germany, could also have been visited by Adolf Hitler and used as a spot for secret meetings.

PICS BY WARREN URBEX / CATERS NEWS - (PICTURED: Smattered with bullets, this is the control room where it is believed allied forces raided the location - bullets still are lodged in the bullet proof glass several inches thick) - An urban explorer has revealed abandoned German tunnels claimed to lead to a secret Nazi weapons testing bunker. After hunting through miles of underground passageways, Warren Tepper, from Hampshire, was shocked by his discovery after climbing through a hole in one of the walls. It is claimed the area was a shelter for Nazis during the bombing from Allied forces and also a bombardment system, where ammunition was tested on steel plates. Inside Warren and co-explorer Matt, found four-inch-thick bullet holes in metal along with similar holes in bulletproof glass, believed to have been from when Americans raided the site. The bunker and surrounding tunnels, that lie beneath Duisburg, Germany, could also have been visited by Adolf Hitler and used as a spot for secret meetings. (WARREN URBEX / CATERS NEWS)

Inside, Warren and co-explorer Matt, found 4-inch bullet holes in metal along with similar holes in bulletproof glass, believed to have been from when Americans raided the site.

The bunker and surrounding tunnels, that lie beneath Duisburg, Germany, could also have been visited by Adolf Hitler and used as a spot for secret meetings.

Warren said: “At first we didn’t really see much, it was just a set of empty tunnels, but then we climbed through a hole in the wall into another part of the tunnels that had been blocked off."

“It was only then that we started to get a feeling for how big and amazing the tunnels were," he added.

“As we carried on walking round the tunnels, we started to find more and more exciting stuff. Then we found the munitions storage and were both really excited at this point, so we carried on in the miles of underground tunnels."

This was followed by a weapons testing room.

PICS BY WARREN URBEX / CATERS NEWS - (PICTURED: Smattered with bullets, this is the control room where it is believed allied forces raided the location - bullets still are lodged in the bullet proof glass several inches thick) - An urban explorer has revealed abandoned German tunnels claimed to lead to a secret Nazi weapons testing bunker. After hunting through miles of underground passageways, Warren Tepper, from Hampshire, was shocked by his discovery after climbing through a hole in one of the walls. It is claimed the area was a shelter for Nazis during the bombing from Allied forces and also a bombardment system, where ammunition was tested on steel plates. Inside Warren and co-explorer Matt, found four-inch-thick bullet holes in metal along with similar holes in bulletproof glass, believed to have been from when Americans raided the site. The bunker and surrounding tunnels, that lie beneath Duisburg, Germany, could also have been visited by Adolf Hitler and used as a spot for secret meetings.

PICS BY WARREN URBEX / CATERS NEWS - (PICTURED: Smattered with bullets, this is the control room where it is believed allied forces raided the location - bullets still are lodged in the bullet proof glass several inches thick) - An urban explorer has revealed abandoned German tunnels claimed to lead to a secret Nazi weapons testing bunker. After hunting through miles of underground passageways, Warren Tepper, from Hampshire, was shocked by his discovery after climbing through a hole in one of the walls. It is claimed the area was a shelter for Nazis during the bombing from Allied forces and also a bombardment system, where ammunition was tested on steel plates. Inside Warren and co-explorer Matt, found four-inch-thick bullet holes in metal along with similar holes in bulletproof glass, believed to have been from when Americans raided the site. The bunker and surrounding tunnels, that lie beneath Duisburg, Germany, could also have been visited by Adolf Hitler and used as a spot for secret meetings. (WARREN URBEX / CATERS NEWS)

Warren said: “It looks like they were firing some big caliber guns down there that would have echoed through the tunnels and been extremely loud.

“I would not have liked to have been down there when the guns were going off inside," he noted. "The sheer size of the tunnels, the largest I have been in yet."

According to research, Adolf Hitler had secret meetings inside these tunnels as he took special interest in the technical development of weapons.

“From what I have read, it was captured by the Americans hence the bullet holes in the bulletproof glass.”

For Warren and Matt, from Finders Beepers History Seekers, this was one of the most impressive sites they have visited.

Warren released the footage on his own YouTube Channel ‘Warren Urbexing’ gathering thousands of views within a few days.

Warren said: “To date, it is the biggest set of tunnels I have explored, and it was my first abandoned exploration I have done outside of England.

“It is also the most amazing one I have done so far because of the weapons-testing facility inside a set of tunnels.”

Warren explains some of his favorite parts of the exploration.

“When we first walked into the weapon-testing room, I thought it was a furness where they heat treated metal and didn't really know what to think until I saw the metal with the bullet holes in the massive bit of metal."

He said: “Then everything fell in place and I realized exactly what it was we were standing in and what it was used for. I was like a kid in a candy store, very excited.

“The bullet holes in the metal said to me that there was big guns being fired down in the bunker and it was scary to think of that going off in tunnels.

PICS BY WARREN URBEX / CATERS NEWS - (PICTURED: Through the miles of underground tunnels lies a secret testing room used during the nazi era used to for weapons testing or training and could have held a secret meetings in winter.) - An urban explorer has revealed abandoned German tunnels claimed to lead to a secret Nazi weapons testing bunker. After hunting through miles of underground passageways, Warren Tepper, from Hampshire, was shocked by his discovery after climbing through a hole in one of the walls. It is claimed the area was a shelter for Nazis during the bombing from Allied forces and also a bombardment system, where ammunition was tested on steel plates. Inside Warren and co-explorer Matt, found four-inch-thick bullet holes in metal along with similar holes in bulletproof glass, believed to have been from when Americans raided the site. The bunker and surrounding tunnels, that lie beneath Duisburg, Germany, could also have been visited by Adolf Hitler and used as a spot for secret meetings.

PICS BY WARREN URBEX / CATERS NEWS - (PICTURED: Through the miles of underground tunnels lies a secret testing room used during the nazi era used to for weapons testing or training and could have held a secret meetings in winter.) - An urban explorer has revealed abandoned German tunnels claimed to lead to a secret Nazi weapons testing bunker. After hunting through miles of underground passageways, Warren Tepper, from Hampshire, was shocked by his discovery after climbing through a hole in one of the walls. It is claimed the area was a shelter for Nazis during the bombing from Allied forces and also a bombardment system, where ammunition was tested on steel plates. Inside Warren and co-explorer Matt, found four-inch-thick bullet holes in metal along with similar holes in bulletproof glass, believed to have been from when Americans raided the site. The bunker and surrounding tunnels, that lie beneath Duisburg, Germany, could also have been visited by Adolf Hitler and used as a spot for secret meetings. (WARREN URBEX / CATERS NEWS)

“Bullets would have been flying all over the place through rebounds and the noise in the tunnels must have been horrific for whoever was in there.

“The holes in the glass were something else; it makes you think how the soldiers must have felt being shot at. Even though it is bullet proof glass, it is still scary.

“Matt and I think it was Americans firing at the Germans during the war to capture the tunnels as just down the road for the village is Aachen, which is famous for the Americans fighting the Germans."

This story originally appeared in The Sun.