In the style of 2e dungeon poster map. a subterranean river has eroded away an entrance into a forgotten dungeon.

Different colored regions denote warring factions or changing dungeon themes.

When I ran this, I had the players fall into A 1 through a collapsing cave roof into a burrow of snakes, fight a dragon section B, encounter a colony of bat people (basically kobolds that fly) sections C, D, E, F, G, H, and then discover a small Myconid colony in section I. Section J, the river also presented random encounters, and serves as an alternate entrance and exit to this map.