“Ryven” was a Myst/Riven fan age made in 1998. It was a series of rendered images stitched together with HTML. Some bits even seem to have used animated gifs for moving pieces of machinery!
It’s long-vanished (I think Geocities removed it due to inactivity even before Yahoo killed Geocities off). BUT, you can still see many of the images from it thanks to the magic of the wayback machine: https://web.archive.org/web/20030402103738/http://www.geocities.com/SoHo/Gallery/3210/riven.htm . The “about” and “making of” pages are pretty great too!
It’s crude-looking by today’s standards, but for 1998 those graphics are pretty sharp–and they were just made and put together by one person in their spare time. I remember being really impressed and inspired when I stumbled across it the first time–it felt like being able to make and explore and share your own ages was tantalizingly close to reality.