Cryptome is a classic source on topics like this [1]. As for what a landing station looks from the inside, Ars Technica had an excellent series [2] on submarine cables in 2016.

[1] http://cryptome.org/eyeball/cable/cable-eyeball.htm [2] https://arstechnica.com/information-technology/2016/05/how-t...

Tom Scott had a pretty good video about them: https://www.youtube.com/watch?v=nl2mQ2HiJZc

Minor correction: Tom Scott's video is great, but I was actually thinking of Motherboard's video which talks about modern undersea cables: https://www.youtube.com/watch?v=iMAThVcqzuk

One of my more ancient bookmarks: http://atlantic-cable.com Mainly history of the first transatlantic link, but also lots on Widemouth Bay and Porthcurno - the two landing stations.

Widemouth Bay is the still active one with a GCHQ intercept nearby.

Tangentially related is this classic long form piece by Neal Stephenson from a 1996 editon of Wired "chronicling the laying of the longest wire on Earth". A great bit of recent transoceanic cable history.

https://www.wired.com/1996/12/ffglass/

https://outline.com/R7vGvk is an outline version of the very good (from 1996...) Wired article, "Mother Board Mother Earth" https://www.wired.com/1996/12/ffglass/