several reasons. a, almost all of them sucks as far as the visual thing goes (atmosphere is one good example of crappy visuals) b, the average joe isnt ready for 3d when visiting a website its to slow and cumbersome. c, most of them requires plugins that very few have, the plugins that are succesful are flash and pdf because they are bundled with almost everything and almost everybody has them by now. so to make an interactive online virtual walk through i would today recomend you to go the flash route, yes flash cant realy handle real 3d (unless you pick up shockwave which has the problem of having to little users) but you can create a virtual walk through that do perform and embed perfectly in your website, and if you would render the scenes ala myst it would still look realy good even tho its just plain 2d with some flash spice. by far your best option today for an online version. Offline well nothing to think about go for all the bells and whistles and pick up a real 3d engine, no question about it if you guys have the budget and development time for it that is.