These cave systems were built in the 1840s for the express purpose of silica mining. The sand in this region is known for being almost pure quartz, making it perfect for glassmaking. Around 40 years later, people found a new use for the old silica mines. Mushroom farming. French immigrants started the practice, and it continued for a century, living through fads of beer brewing and cheese making. After the farms discontinued their use in the 80s, the city sealed them, dumping in tons of excavated concrete waste to fill them up.

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