The most fun websites on the Internet, in my opinion...
ytch.tv - Youtube videos, but in an old school TV format. Rediscover the joy of 'flipping channels' (without the cable bill).
Window Swap - Check out the view from a stranger's window; all over the world. Updates every few minutes. Great for background ambiance.
Radio Garden - Spin the globe and tune in to local Internet radio stations from all over the world. My personal favorite is Scientific Sound out of Ho Chi Minh City, Vietnam. Very oonce-oonce!
Space Awesome - It's like Oregon Trail, but in space. Nobody dies of dysentery, but they do sometimes contract the Intergalactic Plague. Bummer...
Drive & Listen - Choose from over 800 cities and take a little POV drive (or walk) while listening to that city's local radio stations. You've just got to try it.
Geocities Gallery - A gallery of archived Geocities sites, just as they were when the service was terminated. An endless supply of personal and niche websites, handcoded by some of the first folks to 'get on' the Internet. Peak 90's/early internet nostalgia, fascinating and bittersweet.
Colorfle - It's like Wordle, but with colors. That's it.