A series of geocaches honoring the intuitive faculty in the human psyche, which can be so valuable in guiding us through life. These caches are placed along a "Bay Area backroad" that is well known to bicyclists, and the best way to find these caches is by bicycle, which will be the most enjoyable and allow you to savor the quest. But if you like, you can also drive to find them, and there is parking quite close to most of them, although for a couple you'll need to walk about 100 yds from the nearest parking.
Developing your intuition allows you access to what some call the "subterranean realms" of the world. You can regard this either as the subconscious part of the psyche, or perhaps the "Underworld" of mythology.