Grimeton Radio Station, Varberg

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, is home to the only remaining example of an early pre-electronic radio transmitter technology: the Alexanderson alternator.

The station's construction took place between 1922 and 1924. It started operation on 1 December 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, as underwater communication cable connections had once again been quickly severed by nations at war.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons