So while I am on this whole “through a heroquest into your RuneQuest campaign” kick – here’s some ideas:
Pay attention to the calendar. If the characters decide to adventure on a high holy day or Sacred Time, let them find themselves in a magical place. Let them explore it, go to some place else, etc. Give them a magical guide – a Virgil or a spirit coyote (preferably voiced by Johnny Cash) – or someone to pursue (perhaps a White Rabbit). Let them quest until they decide to try to return – maybe they need to find the home of their god, an ancestor, try something just crazy enough to return home, or just say it is over when the mundane time changes.
Tell them that some magical place is even more magical at certain times. Send them to Temple Hill in Sacred Time when it becomes the Spike or the Golden City or whatever. On that day it is possible to take the Crystal Goblet of the Sky from Aether or get your hands on Umath’s Belt of Strength or whatever – if you go to the right place on the Spike. But beware – there are trolls and darkness demons, angry guardians, and giant racoons.
Some healer gives you the Lightbringer Summons and asks you to accompany her to try to heal Arroin at the shore of the Black Sea. The problem is to get there, she needs you to go to the Puzzle Canal during Sacred Time and travel the River Styx past the Devourer and then protect her against the Creeping Chaos.
Now if you strip this down to basics, these actually follow the format of traditional adventures. That’s the key – heroquests are traditional adventures. But the setting, the beings – they all are tied to the Otherworld, making it unfamiliar, dangerous, and magical.