Dungeon-crawling. The core gameplay loop of OSE. Players explore keyed locations described by the referee, who tracks a hidden map. One player typically acts as the caller (speaks for the party) and another as the mapper (draws the map from the referee's descriptions).

Map

Keyed areas (Dungeons, Towers, Ruins, Crypts, Caves...).

• Distances measured in feet (') and inches (").
• Mapped onto squared battlemaps (1 square = 10 feet).
• Typical light source illuminates a 30' radius.
• Encounter distance in a dungeon: 2d6 × 10 feet.

Time-tracking

Turns (10 min). 6 turns = 1 hour.

Sequence of play per turn (the referee runs this loop):

1. Wandering monsters: referee checks if applicable.
2. Actions: party declares one action for the turn.
3. Description: referee describes results; if monsters appear, switch to the Encounter procedure.
4. End of turn: referee updates time records (light, spells, rest).

Per-turn rules:

• Every 2 turns: roll for Wandering Monsters (1-in-6 typical). Distance: 2d6 × 10 feet, moving toward party.
• Every 6th turn (1 hour) the party must rest for one turn, or take -1 to attack and damage rolls until they do.
• Torches burn for 6 turns (1 hour), 30' radius.
• Lanterns burn one oil flask every 24 turns (4 hours), 30' radius.

Main Actions

Describe one action per 10-min turn. Common dungeon actions:

• Move (unknown areas): base movement rate in feet per turn (very slow — accounts for mapping, caution, quiet). Familiar areas: referee may allow up to 3× speed.
• Search a 10' × 10' area for secret doors or room traps. Takes 1 turn. 1-in-6 chance of finding (some classes better). One attempt per area per character. Referee rolls in secret.
• Listen at a door: 1-in-6 chance. One attempt per door per character. Referee rolls in secret.
• Force open a stuck door: chance based on STR. Failure eliminates any surprise the party had.
• Pick a lock: requires character with lock picks proficiency, or magic.
• Rest: required every 6 turns (see above).

Traps

• Triggering: any action that could trigger a trap has a 2-in-6 chance of springing it. Damage is usually automatic (no attack roll).
• Treasure traps (e.g. poison needle on a chest): only specific classes can search for them; chance per class description.
• Room traps (pits, falling blocks): searched as a 10' × 10' area, 1-in-6 to find.

Doors

• Doors opened by adventurers tend to swing shut. Spike or wedge them open.
• Monsters native to the dungeon can usually open doors freely (even stuck ones), unless blocked, spiked, or magically sealed.