Beneath the volcanic hills surrounding Rabaul, on the island of New Britain in Papua New Guinea, an estimated 500 or more miles of hand-dug tunnels honeycomb the earth — remnants of one of the most elaborate wartime fortification networks in the Pacific. Walking the jungle roads, visitors can still spot tunnel entrances boring into the hillsides, many of them open to cautious exploration. Inside, the tunnels range from narrow connecting passages to cavernous chambers that once served as hospitals, barracks, and command centers. Gates visited the site during the very first episode of Expedition Unknown, descending into what he described on camera as "remains of an underground Japanese hospital" to understand the sheer density of wartime wreckage around Rabaul — context that framed his larger search for Amelia Earhart's lost Electra. The area above ground is equally haunting, with rusting anti-aircraft guns still pointing skyward and decomposing landing barges sitting in darkened tunnel chambers.
Japanese forces capture Rabaul and immediately begin digging an extensive tunnel network to shelter troops and supplies from Allied air attacks.
Rabaul reportedly becomes home to over 100,000 Japanese troops, with the tunnels serving as hospitals, command centers, and barracks. Admiral Yamamoto coordinates Pacific naval operations from a fortified bunker here before his plane is shot down leaving Rabaul later that year.
The end of World War II leaves Rabaul's tunnel network largely intact, along with tanks, weapons, bombs, and other relics of the Japanese occupation.
Gates investigates the underground tunnels in Season 1, Episode 1 of Expedition Unknown, contextualizing the site within the broader search for Amelia Earhart's Electra.
Rabaul's tunnel system is broadly recognized by historians as one of the most extensive Japanese wartime engineering projects in the Pacific theater. After seizing Rabaul in January 1942, Japanese forces leveraged both military labor and local conscripted workers to carve a vast underground network designed to protect troops and materiel from the relentless Allied bombing campaigns that intensified from 1943 onward. By most historical accounts, the network included functioning hospitals, communications hubs, ammunition depots, and command facilities — a self-contained subterranean city built to survive an air war.
Admiral Isoroku Yamamoto, who planned the attack on Pearl Harbor, used Rabaul as his primary naval command base during a critical phase of the Pacific War. Historians note that Yamamoto was killed in April 1943 when his transport aircraft was ambushed by U.S. P-38 fighters — the Americans having decoded Japanese communications that revealed his flight itinerary. His preserved bunker near Rabaul remains one of the more tangible relics of high-level Japanese Pacific strategy.
No Wikipedia data was available for this site, so specific figures — including the often-cited "500 miles of tunnels" — should be treated as approximate, based on Gates' on-camera narration rather than independently verified academic sources. What is not in serious dispute among historians is that Rabaul was one of the most heavily fortified Japanese positions in the Southwest Pacific, and that the tunnels played a central role in allowing a large garrison to hold out until the war's end despite being largely bypassed by Allied ground forces after 1944.
Gates investigated the tunnels primarily as framing for the Earhart search — using the density of wartime wreckage as evidence of how difficult it would be to identify any single crashed aircraft in the region. The episode did not advance specific claims about the tunnels themselves, but the on-camera footage offered a visceral sense of the scale of Japanese wartime infrastructure that still lies largely undisturbed beneath the PNG jungle.
Gates describes the tunnel network as containing 'more than 500 miles' of passages beneath Rabaul — a figure that, if accurate, would make it one of the most extensive underground military systems constructed during World War II.
One tunnel reportedly still houses the decomposing remains of massive Japanese landing barges, preserved in the dark and humidity since the end of the war.
Admiral Yamamoto's nearby command bunker retains original writing on its walls, which Gates described as 'all perfectly preserved under all this concrete' nearly 70 years after the war ended.
Rabaul's strategic value stemmed from its natural deep-water harbor, which made it one of the most prized military positions in the Southwest Pacific — and a primary target for Allied air campaigns.
The Rabaul tunnel network is generally accessible to visitors, with several entrances open for self-guided or locally guided exploration along the roads outside town. Conditions inside vary considerably — some tunnels are well-lit and maintained for tourism, while others remain dark, uneven, and home to large bat colonies. Visitors should check current local advisories and consider hiring a local guide familiar with which sections are safe to enter.
Rabaul town is the immediate reference point, though much of modern activity has shifted to nearby Kokopo following the 1994 volcanic eruption. Kokopo is approximately 20 kilometers from the Rabaul tunnel area.
The dry season, roughly May through October, is generally considered the more comfortable time to visit Rabaul, with lower humidity and reduced risk of heavy rainfall that can make tunnel entrances slippery. The wet season brings lush jungle scenery but can affect road access in the surrounding area.
Normandy Beaches, France
Normandy Beaches represents another major theater of World War II that Gates investigated, connecting through the shared theme of large-scale wartime history and the physical remnants left behind.
Lake Otjikoto
Lake Otjikoto is another site where wartime materiel — in that case, German weapons dumped at the end of WWI — was submerged and left largely intact, paralleling the Rabaul tunnels' role as an undisturbed war relic site.
Australian Outback
The Australian Outback appears in Expedition Unknown's Earhart investigation arc, which is the same episode and search that brought Gates to the Rabaul tunnel site in the first place.