As long as the web has been able to display more that plain text, there have been pages that are "useless". Sites that aren't for the dissemination of information or provisioning of a service. Some are "art" sites; not websites that are used to display or document art or artists, but the website itself is made to be an interactive art piece. Then there are timewasters - sites that show interactive visualizations, puzzles, mini games, etc... These rose to prominence in the "Flash" era, but thanks to modern CSS and JavaScript live on.

Here's a collection of "useless" websites I've recently found and have enjoyed for years. Browse at your own risk, there are sites with flashing light and sound warnings:

superbad - an early art site
the useless web - randomized links to a wide variety of "useless" sites
paint toys - the name says it all.
staggering beauty - art? timewaster? sure.