The Mound: Omen of Cthulhu features a locked map system that expands through the collection of Fort Logbooks hidden throughout jungle expeditions. These logbooks are located exclusively within small fort encampments scattered across the game world. The second expedition serves as a guided tutorial that walks players through the process: starting from the shore, exploring the right flank to gather supplies, then moving left to acquire a medallion that displays all island valuables before finally navigating past enemies and locked doors to reach the fort containing the first logbook.

Once a logbook is successfully obtained and the player returns to their ship, the game map updates to display white markers indicating the locations of additional logbooks throughout the explored jungle areas. This progression system creates a gameplay loop where each collected logbook both reveals more of the world and points toward the next collectible, encouraging continued exploration and resource gathering during subsequent expeditions.