The Dens are set in the Great Wall of China and represent early atmospheric forums / blogs. You can no longer create public dens but they are still active and act like a legacy to this time of communication online.
Note the subscription feature (the bat icon), a feature still used today in forums but invented by Dan Zen – although it is unknown if other subscription systems predated them.
The Den technology was also later used for communal story telling in the Blimp Race series where people hurled curses at other blimps and planned their strategies. And in Shrink Ray where players were shrunk and stuck in a bottle. And as forums for games like RichDeck, Motogami and of course the Billionaire’s Den in Password Paradox. The Hand Game was a collaborative effort that used the technology.