Rip Surfer X
Cross-country skiers have the Nordic track. Cyclists have all manner of indoor trainers. Rock climbers have indoor climbing gyms and escalator-like moveable walls. Hell you can even snowboard in indoor manmade, climate controlled mountains (it's huge in Japan).
Until recently, however, surfing indoors was a laughable proposition. And to be fair, it still is, but for the vast majority of those who live in parts of the country without access to surfable coastline, a new training product called the Rip Surfer X promises plenty of the undeniable core fitness benefits of surfing without ever having to get salt water up your nose.
The Rip Surfer X uses a broad, stable "board" design suspended on elastomer bumpers that require some degree of balance to steady, replicating the isometric benefits of balancing on a surfboard—if not working a board into a wave face.
From simulated carving, to popping up, to repeated duck-dive pushups, its seems entirely possible to work up a sweat fooling around on one of these. Good training for the real thing? Sure, why not? But if you thought "SUP Longboarding," on dry land, on a bike path was silly, you haven't seen nothing yet.
The Rip Surfer X will be available in a home version soon, but until then look for a demo at a gym near you.