.... or The Dangers of Walking on Railway Lines.
In 1895, while walking through the tunnel on his way home, Mrs W.E.K.A.'s great grandfather was killed by a train.
The train from Dunedin ran over him on the outward trip, then again on the return trip, after which they stopped to investigate.
If you want the gruesome details - Papers Past: The Chain Hills Tunnel Accident, ODT 29 Aug 1895 page 8.
The cache is a 200 ml Sistema hidden in an alcove towards the southeast end of the tunnel.
A torch may be useful for finding the cache, but is not essential as the tunnel is well lit.