sites for virtual tourists
The 'net is full of examples of invented worlds. Many were designed specifically for role-playing games, but there are quite a few which stand as independant creative works, with no other purpose than to simply exist.
Mark Rosenfelder's Virtual Verduria, which is mentioned elsewhere on this site (under conlangs if you must know), should be paid a visit by any self-respecting virtual tourist. One of the best examples of a virtual world, it is a huge site, and still growing.
M A R Barker's Tekumel, Empire of the Petal Throne is another famous example. The web-site is graphic-intensive, but very beautifully done.
Worlds in the Net has links to huges numbers of web-sites of imagined worlds. Many are part of rpg campaigns, but some are just stand-alone creations, with no other excuse for their existence.
The 'net is full of useful tools for people who want to create their own imaginary worlds. Here are few that I have come across.