In late 2011, as a big fan of Dungeons & Dragons, 3rd Edition, I started adapting the rules for co-operative play without a dungeon master. Along the way I've managed to automate or clarify some of the excellent rule system. Here are some of the resources I've found or created to be most useful.
In these pages I hope to construct a fully playable set of rules for solo dungeon adventuring based on Dungeons and Dragons 3rd Edition.
It's handy to have a reference to the most important and most common rules of combat. I wrote up this 2-page reference (version 1.0): Combat Options.
Use the terrain to make fights in Dungeons & Dragons more interesting! Even something as simple as a doorway or the corner of a wall can help in a fight. Keep the following common forms of cover in mind when up against a humanoid's missiles or a dragon's breath attack:
The Monster Manual describes an ability that many monsters have called "Improved Grab", but the rules are markedly confused. I made an attempt to interpret the letter and spirit of the ability in this document: Improved Grab Combat.
An adventure involving travel through any type of wilderness would benefit from a familiarity with different types of terrain. Picture J.R.R. Tolkien's novels, where the characters walk vast distances though plains, forests, mountains, and marshland. Topographical features are called landforms and they have been comprehensively named and described by experts in the field.
The description for the Druid Spell "Detect Snares and Pits" (Core Rulebook I, Player's Handbook, page 194) says that the spell will detect "primitive traps constructed of natural materials (man traps, missile traps, hunting snares, etc.)". However none of these are described elsewhere in the core rulebooks.
The 1911 Classic Encyclopedia Project has a comprehensive description of historical and traditional man-made traps. If the page ever disappears I'll find it again or paraphrase the copy I have. These common types of traps are likely to be encountered by normal adventurers, and they allow for characters (like Rangers and Druids) and enemies (like Kobolds, Goblins, and Gnolls) to construct simple traps for everyday use, rather than expensive, sophisticated traps that you'd only expect in some dark castle built by an evil wizard.