Here is some more information: https://en.wikipedia.org/wiki/All_Red_Line
And one of the old cable huts still exists: https://en.wikipedia.org/wiki/Pacific_Cable_Station
And one of the old cable huts still exists: https://en.wikipedia.org/wiki/Pacific_Cable_Station
(There's also the https://en.wikipedia.org/wiki/Minack_Theatre built into the cliff face nearby.)
(I've been to the theatre a number of times but never convinced my in-laws to visit the Telegraph Museum.)