First sewage plant underground

According to Official Guinness Records,

The Henriksdal plant in Stockholm, Sweden was the world's first major waste-water plant to be built underground. It was built between 1941 and 1971, and involved the excavation of nearly 1 million m³ (35,300,000 ft³) of rock. It is now being enlarged, with the extension due for completion in 1997.

For a complete list of 1971 records, please visit 1971 Guinness Records in Sweden.

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