When the tide goes out, a hidden world of marine life is revealed—full of strange and beautiful creatures clinging to rocks or tucked beneath seaweed. Tide pooling offers a rare glimpse into this world, and in this guide, I’ll take you to my favorite spots near San Francisco, with tips on when to go, what to look for, and how to explore responsibly.

Every year, starting in October, thousands of monarch butterflies embark on the journey of their lives, escaping freezing temperatures and seeking the shelter of the mild climate along the California coast. It’s a journey that none of the travelers have ever undertaken before—without a map, without a compass, and relying solely on their instincts. This repeated journey is made by a unique generation—a generation with lives so drastically different from those of their parents, grandparents, great-grandparents, and even great-great-grandparents. All of this happening simply because they were born in the fall.