This requires a Windows or Linux PC running WalkAbout3d Viewer available here for free. The offline version has some very nice advantages over the online previews like better navigation and stereoscopic 3d support for 3dtvs, 3d-ready projectors, the Oculus Rift and various other home made systems*. To run the WalkAbout3d Viewer in non stereoscopic mode, go to Settings->Stereo and de-select Stereo.
Linux users can run downloaded content with the WalkAbout3d Viewer using Wine. This works very well on Ubuntu 13.10 and should work fine under other distributions as well.
Mac users will have to make do with the online previews for the time being. One possible workaround, yet to be confirmed, would be to run WalkAbout3d Viewer using Parallels or similar windows emulation software. Please let me know if you try this successfully!
Smartphones. Some will do it and some will not. If you get a 360 rotationable animation that's a sign your phone belongs to the latter. Try another phone or go find a computing machine.
*Nerds might want to go all out and set up their own stereoscopic display