Kola Superdeep Borehole. Source: Read more about the hole: en.wikipedia.org/wiki/Kola_Superdeep_.... reached lli, (403591?) just to , geep they) cauld drill?!. Maybe they were just bored. Kola Superdeep Borehole Source: Read more about the hole: en wikipedia org/wiki/Kola_Superdeep_ reached lli (403591?) just to geep they) cauld drill?! Maybe they were bored