Sonar Panic

Sonar Panic is the deep-sea game of the Panic series: a bathyscaphe sinks through an underwater rift in total darkness and only sees with sonar. Each ping draws the walls in cyan lines for a moment, but it can also be heard, and the mines it touches wake up and head for the spot you pinged from. Seeing has a price: every ping can save you from one danger and create the next.

The rift is randomly generated and always passable: shafts, meanders, chambers with rocks, chimneys, stalactites and forks with a dead-end branch. Three zones, bathyal, abyssal and hadal, with creatures that hear the ping from afar, capsules only the echo reveals and a shared records table. Free, no sign-up and installable as an app.