In 1990, mining stopped at a 55-metre-deep Swedish limestone quarry; a year later, an opera singer discovered its remarkable natural sound, and it became Dalhalla, now drawing 100,000+ visitors each summer

• 55-meters-deep Swedish limestone quarryWhen mining stopped at an isolated limestone quarry in central Sweden in 1990, the local area was left with a 55-metre-deep industrial pit cut into the pine forests outside Rättvik.
• Just a year later, a former opera singer discovered that the abandoned quarry had remarkable natural acoustics.
• Today, the former mining site has become Dalhalla, an internationally known open-air concert venue that attracts more than 100,000 music fans to Dalarna every summer.