The limestone ridge of Shoushan presented the Japanese colonial administration with a problem and an opportunity simultaneously. The ridge separated the fashionable hill park at its crown from the waterfront neighborhoods below, and connecting them required cutting through solid rock. Excavation began in 1927 under Sanjiro Umino's direction, a technically demanding project given the equipment and methods available at the time. The tunnel was finished by 1928, though it did not open for public use until 1933 as the Kotobuki-yama Tunnel — named for the park it served. The structure that Umino's crew produced is 260 meters long, 6 meters wide, and 3.6 meters high, with arch-shaped concrete entrances at both ends. Three sections make up the tunnel: a front section, a middle section, and a rear section, the last of which would later acquire its own secret history.

During World War II, as American air raids became an increasing threat to Kaohsiung's port and military infrastructure, the tunnel's rear section was converted into a Japanese combat command center. The location made strategic sense: buried inside limestone, invisible from the air, with ventilation and water supply already in place. The secret section is U-shaped and 100 meters long, extending beyond the main tunnel corridor. Designed to provide a view in all directions through the rock — likely via communication lines and observation points connected to external positions — the command center was built to function as the Japanese military nerve center for the region. It had bathroom facilities, dormitory space, electricity, and a ventilation system, designed to sustain operations during prolonged bombardment. The space could accommodate up to 2,150 people, though as a command center rather than a civilian shelter its occupants would have been military personnel.

After the war, the tunnel passed into the custody of the Republic of China government and fell into a kind of institutional ambiguity. The Kaohsiung City Government renovated the middle section in 1990 and 1991, a partial effort to make the passage usable again. On 9 April 2004, the city declared the tunnel a historical monument — official recognition of what the structure represented, even as the question of public access remained unresolved. In 2008, the tunnel entrance was demolished, a setback that set back physical access further. Then, in 2017, the momentum shifted: a section of the tunnel underwent full renovation as part of the Hsing Pin Plan city restoration program, with the front section receiving landscaping work. The tunnel was officially opened to the public on 11 November 2017, timed to coincide with the 30th anniversary of National Sun Yat-sen University, whose campus adjoins the tunnel's eastern entrance.

The tunnel that opened to the public in 2017 is not a bare historical passage but a designed experience. Lighting installations and projected images animate the walls, turning a functional throughway into something more contemplative. The effect shifts depending on where in the tunnel you stand: the arch-framed concrete of the entrances has a solidity that the decorated interior softens, and the secret U-shaped section — finally visible to the public after decades of restricted access — carries a different atmosphere entirely. The dormitory alcoves, the electrical conduits, the ventilation systems: all still legible as infrastructure built for people under threat. Walking through the tunnel means moving through multiple eras at once, from the Japanese park builder's practical vision to the wartime planner's defensive calculations to the contemporary city's decision to make art of what remains.

The Sizihwan Tunnel connects two different kinds of Kaohsiung. On the eastern side, the National Sun Yat-sen University campus occupies a hillside above Sizihwan Bay, a curved inlet sheltered by the Shoushan ridge, popular for its sunsets and its seafront promenade. On the western side, Linhai Road runs through Hamasen — the old Japanese-era harbor district, whose name means roughly "front of the sea" — a neighborhood of old merchants' houses, temple alleys, and the Hamasen Museum of Taiwan Railway. The tunnel is walkable from Sizihwan Station on the Kaohsiung MRT, placing it within easy reach for anyone exploring the western waterfront. It is a short passage, physically, but the distance it bridges — between the modern university, the wartime past, and the old port city — is considerably longer.