Grimeton Radio Station

In the 1920s, Sweden realised its reliance on other countries' underwater cable networks and decided to build a high-power radiotelegraphy station after the temporary loss of those vital links during World War I. The station, Grimeton Radio Station, was home to the only remaining example of an early pre-electronic radio transmitter technology: the Alexanderson alternator. The station started in 1924, after its construction in 1922-1924, and immediately took over 95% of the Swedish telegram traffic to the United States. During World War II, it was one of Sweden's few telecommunication links to the rest of the world.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons