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

Anyone visiting the South West of the UK should go visit https://en.wikipedia.org/wiki/PK_Porthcurno (https://pkporthcurno.com/)

(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.)

My wife and I were visiting County Kerry in SW Ireland last summer. We were on Valentia Island and quite by chance walked past the telegraph building where the first transatlantic cable came ashore. Only marked by a (very interesting) plaque describing its significance.