Places that are hard to get to and harder to do badly. Antarctica. Galápagos. Bhutan. Papua New Guinea. The trips you only do once, that have to be right the first time.
Expedition trips don't forgive a poorly chosen vessel, a wrong-season departure, or a guide who knows the route but not the place. The cost of getting them wrong is unusually high, partly financially, partly because most clients can't easily go again.
The work is unrelentingly specific. Which ship for Antarctica matters more than which itinerary; the small expedition vessels are not interchangeable. Galápagos by motor yacht versus catamaran versus larger cruise ship is three different trips, and the right answer depends on whom you're travelling with. Bhutan done in five days is a different country from Bhutan done in fourteen. South Georgia is the bit of the Antarctica trip most people get wrong by leaving out.
The properties on expeditions are often vessels rather than hotels, which puts even more weight on knowing the operator, the captain, the expedition team, the cabin choices. The hotels at the start and end of expedition trips matter disproportionately: the seventy-two hours either side of a hard journey are when most things go wrong.
The bookings happen long before the trip, sometimes eighteen months. The conversations begin earlier still.
The other five
When you're ready