Deep in Snowdonia lies a lake across which an island once floated. In folklore this is not unusual. St Brendan’s Isles drifted around the globe for centuries, and seven of Britain’s canonised saints apparently floated to our shores on a sod. But in this case the island was real, and unusual enough for Edmund Halley the astronomer to swim out and see for himself in 1698. He described a piece of turf broken loose from the bank and buoyed up by the lightness of “broad-spreading fungous roots on its sides.”

Read more in the November 2018 edition of BBC Countryfile Magazine