While the concept of building a doomsday-style secret bunker may seem evidence of a somewhat pessimistic take on mankind's future, Oppidum founder and chief executive officer Jakub Zamrazil insists that the company takes an "optimistic view of the world", but adds that it is nevertheless wise to be prepared in an "uncertain world".

To that end, says Zamrazil, "an Oppidum provides peace of mind". And we should certainly hope so. While the baseline price for an Oppidum bunker is $10 million (£8m), their state-of-the-art L'Heritage model costs in the region of $100 million (£80m), according to the company's Head of Communications, Tom Grmela. Models without the luxury extras, such as staff quarters, start at around $60 million (£47.9m).

Peek inside the secret bunkers built for the world's wealthiest