So when thinking about any heroquest, I start by looking at one of Greg’s old Hero Plane maps. This is a map of archetypes – and not the same thing as the Mythic Maps (which show the relationship of known mythic events and how they shaped the world). I think of this like a guide to Dreams or even something like the Sefirot. Perhaps our quest will be to travel from the Home of the Storm Lord over the Bridge through the Calm Air (making your way past the Four Winds) across the Sea of Flames to make your way to the Sky Palace in order to secretly aid the Imprisoned Queen and bring her back to the Womb. We associate these places with mythic events and places (is the Womb the great temple of Ezel, the Paps, or just the Earth Temple basement?), but you create your own story when you go there.
Then arm the players with a few stories. Maybe they learn a secret from a God Learner scroll that it is possible to befriend Mr. Racoon who can sneak you into the Imprisoned Queen’s chambers. Or perhaps they learned something in the Cradle that lets you travel across the Black Sea to the River Styx or realize that they already saw this scene in Kakstan’s Art Gallery. However you do it, try to tie this into their experiences in the game.
If they have already been on a heroquest, even better – rope that experience into this.
And always throw in something unexpected that shouldn’t be there. Let the White Moon goddess be their guide instead of Voria. Have the Lord of Trees refuse their offered flower (the one the scroll said would give you passage).
In short, try to treat the Hero Plane as a sand box that constantly changes. It is the realm of dreams and spirits. The stories of others can help guide you but are only glimpses, like reading the dreams of others. Treat the Hero Plane as its own place, one that constantly shifts, but also one that gives us visions of the foundations of Glorantha.
A key bit of advice – resist the temptation to predefine these locations/events beyond the archetypical. Let your players define them through their experiences!
Note that many even most of the entities you might encounter have no cult, appear in no stories except your own. We can have Mr. Raccoon and Drunken Frog, Mirror Man and the Red and White Twins, Stardust Dragon and the Sulky Albino, intermixed with Storm King and Earth Lady.