The world's largest lake was born 75 000 years ago following the eruption of a super volcano, whose crater collapsed on itself, creating a huge pit that filled with water. Lake Toba, a genuine inland sea whose bluish-mauve water is fringed in steep cliffs, boasts unparalleled dimensions: 100km long, 35km wide and up to 505m deep. Take the time to swim in this natural wonder. In the centre of the lake is the island of Samosir, inhabited by the Toba and equivalent in size to Singapore.