I found myself in the seedy port town of Keelung near the end of my round-the-island bicycle tour of Taiwan in 2013. Later on, after dinner was done, I went out wandering the labyrinth of night—and, on the far side of the railway line near Sānkēng Station 三坑車站 I noticed the entrance to a tunnel running beneath the hillside. Curious, I hunched down (the clearance is only around 175 cm) and made my way through. A minute later I emerged on the other side, somewhat disoriented, though I quickly regained my bearings.
Since then I have revisited this mysterious passageway several times. When I became somewhat more proficient in reading Chinese the plaque over the southern entrance helped me unravel the story. Formally known as the 100-Year-Old Bomb Shelter 百年防空洞, this peculiar feature of the Keelung urban landscape was originally constructed in 1903, ostensibly for patients at a nearby military hospital (now the site of a school). Later on, in World War II, it also served as an ammunition depot—back when Americans were dropping bombs on Taiwan.
After taking control of Taiwan the KMT continued to use the tunnel for military purposes but it was eventually abandoned. From what I’ve read the unlit tunnel became a public health menace, accumulating rubbish and attracting intravenous drug users. Only recently was it cleared out and transformed into a modest cultural attraction and quirky pedestrian shortcut.