You see many strange and wonderful sights in the Galapagos. T-shirts with Darwin's mug on them; giant manta rays "flying" gracefully underneath while you're snorkelling; the tiny but utterly unafraid bird that takes a liking to your shoelaces; a dozen or more frigate birds hitching a ride on the ship's rigging because they can't take off from water.
You might see, as we did on a group tour last year, a frantic hunt for one bloke's dentures, lost in the water off a beach where grey marine iguanas, sloughing their skin like old velour sofas left out in the rain, basked in the sun next to nonchalant seals.
You might also laugh at the reaction when one of the guides leading a snorkelling group points out something in the water and is shocked to see his entourage swim en masse for the beach. As someone said afterwards: "You just don't shout 'shark' to a bunch of Australians, no matter how small it is."
But nothing ... nothing can prepare you for the spectacle that greets you on the final night aboard the MV Santa Cruz, a 72-metre airconditioned deluxe cruise ship that ferries up to 90 passengers around the 18 major islands of the Galapagos archipelago.
And that's the sight of the ship's captain, Eduardo Neira, a handsome, moustachioed man in the mould of Omar Sharif with salt-and-pepper hair and immaculate bright white trousers, white shirt (complete with epaulettes), white shoes and white socks climbing on to the stage in the bar, taking up a guitar and settling himself down on a tall stool like some louche lounge singer from the '50s.
Outside, the sun is sinking in a glorious riot of apricot, pale-blue and silver, but inside the heart sinks at what's coming next, especially when he is joined by the lady who runs the souvenir shop and reception, and is about to provide backing vocals.
Usually, when anyone whips out a guitar on such occasions I head for the hills or the bar, but both options are stymied as I'm in the middle of the ocean and, um, already at the bar (happy hour, too, so I was stuck).
And then he started singing. And, boy, could he sing. And play the guitar. Michael Buble needn't start looking over his shoulder just yet but it wasn't the shipwreck I was expecting.
Starting with The Girl from Ipanema (the Harry Belafonte version, of course), the good captain wove his way through Guantanamera and a hilarious La Bamba ("Yo no soy marinero, soy capitan, soy capitan") which morphed perfectly into the Beatles' Twist and Shout and back again, when the captain pointed out that the Fab Four stole La Bamba.
By the time he got to Leaving on a Jet Plane, feet were tapping all over the place and he finished with a rousing medley of A Hard Day's Night and (I Can't Get No) Satisfaction before asking for requests.
In the end it came down to Gwen Heron, of Phillip Island in Victoria, who asked for Light My Fire by The Doors - a hit in 1967 when Gwen was a spring chicken of about 39 years young.
The captain is given rousing applause, thanks us for coming, hopes we had a good time in the "wonderful Galapagos Islands" and heads off to, hopefully, steer the ship in the right direction.
The next morning, as we reluctantly disembark, there are copies of the captain's CD for sale at reception. How I wish I'd bought one to go alongside my tasteful blue-footed boobies T-shirt.
The writer was a guest of Captain's Choice; see captainschoice.com.au.