A suspended, transparent (plexiglass) wheel partially full of water. The swimmer climbs in through the middle, and the wheel spins just fast enough (or slow enough) to stop the swimmer from leaving the water. [A combination of computer vision and powered motors accomplishes this)
[Edited with feedback from comments] -- The wheel will have to have some sort of hidden (or not so hidden) "endless-pool" like mechanism to keep the water moving independently of the rotation of the whole assembly in order to keep the swimmer stationary. So you can think of this more as a suspended, transparent endless pool with the hamster-wheel spinning for effect. I still think it'd be cool to look down on people while swimming. --
The wheel can be on a sturdy (yet portable) stand or be suspended from a ceiling for a more permanent installation (the latter requires some interesting ladders to get in or out).
The advantage is that the swimmer gets to see what's going on outside. The "pool" can also be drained and stored when not in use. It might also be a space saver for people or gyms that would like to take advantage of the 3rd dimension...
A whole gym full of these things suspended from the ceiling with people in them would also look kind of trippy...
[The credit for my idea goes to my cousin who likened swimming in a pool to being in a hamster-wheel.]-- cowtamer, Apr 18 2009 Endless Pool http://www.endlesspools.com/index.htmlA sort of "swimmer's treadmill". [jurist, Apr 18 2009] Prototype This: Waterslide Simulator http://www.grandide...terslide-simulator/ [jutta, Apr 18 2009] A visual. http://en.wikipedia....html?curid=1075659 [2 fries shy of a happy meal, Apr 18 2009] Sorry, no. In the proposed design, the water would stay at the bottom of the wheel. It would not be moving past the swimmer . . . or rather the floater.-- baconbrain, Apr 18 2009 The type of pool that [21Quest] describes is frequently marketed as an "Endless Pool" (see link), or in varying forms as a "SwimEx" or "Hydroworx" pool.
Assuming that [cowtamer] could design a large half-filled watertight and zorb-like sphere with piped in atmospheric oxygen, why couldn't it be suspended from the ceiling on a horizontal external axle and spin freely from the momentum of an internal swimmer? I don't think any motorization would be required if the sphere were actually large enough to accommodate the forces of the swimmer's wake and recirculating currents. But, at least in my mind, it is probably important for the shape to be spheric in order to accomodate this effect. [Edit: Ah, it's the old rolling goldfish bowl problem again, isn't it? The goldfish never has enough weight displacement in the water to shift the center of the bowl's gravity, right?]-- jurist, Apr 18 2009 reasonably sure this wouldn't work but I wish it would [+]-- FlyingToaster, Apr 18 2009 What baconbrain said. Add a pump to move water from the back to the front (ala endless pool), and you're getting somewhere. Erm. Or not, as the case may be.
I visited an "endless pool" owner one day and tried it out - it wasn't that fun. It seemed more like swimming against a force, rather than through a truly endless amount of (otherwise still) water. Like someone is pushing you back by pointing a hose at you. I'm guessing that it would be quite difficult to actually move a swimmer's surrounding water as quickly as a swimmer would move through it.
A recent episode of the US Discovery Channel show "Prototype This" featured a water slide simulator wheel that worked on very similar principles - but instead of swimming through the interior of a hamster wheel, the rider slid down its edge. It looked to be quite a fun monstrosity. (See link.)-- jutta, Apr 18 2009 [2 fries'] + [jutta's] link = I think I get it now. +-- blissmiss, Apr 18 2009 random, halfbakery