One sunny summer afternoon, a group of 30 people line up to enter a mysterious concrete tower on a small island off the coast of Taiwan. They are not curious tourists waiting to take a peek at the three-storey structure made up of 48 loudspeakers. In fact, they are there on an artistic mission – members of a local choir taking turns to sing into the microphone inside the tower, part of a one-off performance at a site that was once the embodiment of sonic power.

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It is the Beishan Broadcast Wall on one of Taiwan’s Kinmen Islands, just 2km (1.2 miles) away from China’s Xiamen city. Built in 1967, the broadcast wall used to be a strategic military stronghold that played a key role in sonic warfare across the straits, blasting out anti-communist propaganda. Nearly three decades after the tower stopped functioning, a group of artists based in Berlin and Taiwan are turning the forgotten historical site into an experimental art stage that investigates the idea of ‘territories’ beyond the conventional definition.