Getting lost in the dark

This guide provides a modular hex-crawl framework for extended journeys through the Underdark.

Travelling through the Underdark is a daunting task. Adventurers can quickly lose their bearings in its twisting tunnels. Mechanically, exploration is often reduced to rolling a random direction and continuing until the party encounters a familiar landmark, but little structure is provided beyond that.

It expands those mechanics with a high-level, hex-based travel system designed for extended exploration through the labyrinthine tunnels of the Underdark. It will help reinforce narrative structure, introduce meaningful navigation decisions, and ensure that each travel period can lead to discovery, danger, or both.

Creating agency through navigation and choice will keep players engaged and can keep exploration interesting and consistent as they delve deeper into the unknown.

This guide is an expansion of the Wilderness Travel Guide, and the rules presented are designed to work in conjunction with it. Use the core mechanics from the Wilderness Guide—such as travel periods, exhaustion, and weather—in tandem with the hex-based system to support long-term exploration through the Underdark.

What’s in this Guide

This guide provides modular, optional mechanics to enhance wilderness travel. Use as needed to add immersion, challenge, and variety to journeys.

• Terrain & Travel Pace. Base activity DCs, pace effects, and terrain modifiers unique to the Underdark.
• Hex Grid Exploration. Framework for building a modular hex map, rolling terrain, and placing narrative landmarks.
• Travel Tasks. Rules for navigating, searching, tracking, foraging, and keeping watch—each with modifiers and examples.
• Hidden Features & Terrain Tables. Subtype and discovery tables to enrich each hex with unique landmarks and details.
• Random Encounters. An encounter composition system that fits any pacing or threat level.
• Environmental Complications. Rules for sudden hazards—such as fog, cave-ins, fungal blooms, or ambient dread—to create tension between encounters.
• Weather in the Deep. Rules for evolving fog conditions and their effects on exploration and perception.
• Quick Reference Sheet. An at-a-glance summary of the mechanics.
• Hex templates. Blank and pre-filled, printer-friendly PDF.
• Hex icons. SVG and PNG.