Active Worlds (see https://www.activeworlds.com/web/) is maybe one of the oldest virtual worlds still around.

Active Worlds (see https://www.activeworlds.com/web/) is maybe one of the oldest virtual worlds still around. Founded in 1995 it's over 20 years old. I have sometimes checked in as a tourist to see what's happening. There are lots of locations to visit, though the graphics looks very different from you'd expect in, say OpenSim, or even Twinity. As a tourist you can select boilerplate avatars, including a bird if you want to fly about.

So far as I know, there's a LOT of active worlds in this, as per the map below.