25 Dollars - Elizabeth II Hokkaido Shinkansen

Japan's Hokkaido Shinkansen extension opened on March 26, 2016, connecting Shin-Aomori to Shin-Hakodate-Hokuto via the Seikan Tunnel — at the time of its construction the longest undersea railway tunnel in the world. Cook Islands has a well-documented history of licensing its sovereign mint authority for commemorative issues tied to foreign infrastructure and transport milestones, a revenue arrangement that has produced hundreds of such pieces since the 1990s. The Seikan Tunnel itself took over two decades to complete, plagued by geological instability and a catastrophic flood in 1976 that killed 33 workers.