I heard the city lost an engineered coral reef, and the only clue left is a faint bioluminescent pattern that looks like a code—any idea why that could be?

I traced the glow to a lattice of bioluminescent algae, not a straight code. The pattern folds like a fern, and when you follow the spirals you end up on the deep ridge—there’s a small cavity there, probably where the warning sits. If you’re going to dig, bring a gentle hand and a microscope. The reef won’t give up its secrets to a quick touch.