There are some locations so exclusive that mere mortals (the poor) will never lay eyes on them: the royal suite of the Ritz. The Holy See of the Vatican. The US president's war bunker.
Photographer Nick Gleis has crossed one mystery off that list. For over 30 years, his work has lifted the veil on the world of private jets - the toys of royalty, heads of state and billionaire businessmen.
Here's a selection of some of the most exotic interiors to grace the skies: