Drowned railroad tracks lead to an abandoned passageway nearly lost within a cascade of leafy greenery. Once inside, an enchanting blue glow illuminates the dark, dank tunnel.

Officially called the Metropolitan Tunnel, this underground passage was built in the 1880s. Its use was short-lived, as it closed in 1915 after years of soot and smoke built up within the space and made it dangerous for the trains’ crews and passengers to pass through.

One end of the tunnel became sealed shut so it could become a reservoir. The north entrance, too, became blocked from years of mucky debris building up outside. The whole tunnel was nearly hidden behind a thick veil of lush flora. Before it was drained and partially cleared in 1995, the entire passageway was full of stagnant water.

But the tunnel wasn’t completely abandoned during this time. A colony of glowworms—one of the largest in all of New South Wales—moved in and made its home on the roof. The insects illuminate the stale, inky air like a constellation of blue-green stars.

The tunnel still floods fairly frequently. On days where the water level is particularly high, people pass through the small waterfall that often tumbles across the entrance after heavy rains with pool floats or inflatable canoes in hand. They then paddle deep into the darkness until they reach the spots where the ceiling becomes brightest with the soft glow of the bioluminescent bugs.