Now that I've put down train travel, I re-read benoit's question as one that I've been thinking about asking the jaded travelers here: having been around a couple of times, where are those land-based special adventures?
The road north from Banff, Canada follows the spine of some really nice mountains, with not too strenuous hikes to look at glacial flows here and there, and a tourist ride onto the glacier at Athabascar (?). Unfortunately, it's pretty far off an OW route. And read and heed the "bears have eaten tourists here recently" warnings they nicely post at the trailheads.
During fall and spring, Chateau Lake Louise and its attendant glacial lake and the environs are some of the prettiest places on the planet, and there are plenty of places to walk. In normal times, though, you'd avoid it during the summer season because of crowds.
My Tranzalpine snot notwithstanding, ZQN is a worthy place to land. The light-plane trip to Medford sound is worthy, and the couple of glaciers on the West cost (Franz Josef, Fox) provide an interesting juxtaposition of tropical rainforest and glacier.
Australia's Heron Island, especially reached by Marine Helicopter's service, is a worthy stop, especially if you're a diver.
The train from Bangkok south was a worthy trainsman's adventure, passing through the backyards of "real" Thai.
Indian trains are surely an adventure. It's been a long time since I used them to any great extent, but I suspect there's still a lot of colonial-era equipment running a bit farther from population centers.
It's not an OW port as present afaik, but flying from KTH to Lukla (an STOL strip at 10kft or so, beginning of the trek toward Everest) is likely to provide a bit of adventure. Too bad the country isn't more stable and CX or BA isn't serving.
I'd suggest investigating the politics of the Blue Train before booking it. I'd guess the clientele (and service) have changed since its heyday, and although I revere South Africa for its game parks, geographically it's only so-so. And it's a long ride.
In first class, Eurostar is a decent ride.
We took a milk run from Venice to the city south of Cinque Terre. The cars actually had those accordian-doors that city trams and busses had, in another age. People-watching was interesting, and the scenery was lazy-day sleep-through-it stuff, best enjoyed after too much lunch and wine.
In central/eastern Canada you can (could?) take a train from civilization to the southern tip of Hudson (James) Bay. I've never done it, but I suspect it meets the test of "interesting". Also more-or-less impossible to get to.
Speaking of quaint, a train lover *must* take the train from BKK to the city. The Hong Kong Express it ain't, but except for getting your bags down the metal stairs to the station, it's just as convenient, and costs about a dime if I recall. Fully-airconditioned cars, too, if the windows are open. I think the exit is on the way to the Amari airport hotel, but someone will be glad to point it out to you. You won't find it by following the crowds.
Anyone else? In any case, happy trails to all. (The mileage-runners who never leave the airport, will have no idea what this thread is about, but it's about time we talked about this side of travel.)