When climbing in a difficult or pressured situation, the referee may require a DEX check to avoid falling.

Very steep or sheer surfaces are normally impossible to climb without specialised equipment. Some characters have class abilities which allow them to attempt to climb such surfaces unaided.

Characters will usually want to bring a source of Light with them on underground expeditions. Typical Light sources enable normal vision within a 30′ radius.

All non-human monsters and many demihuman races have a special kind of vision that allows them to see in the dark. This is called Infravision.
Heat tones: Characters with Infravision can see heat tones, with warm objects (such as living creatures) appearing bright, cold objects as black, and cool objects as grey.
Reading: It is not possible to read in the dark with Infravision, because fine detail cannot be perceived.
Range: Infravision works within a limited range (60′ for monsters, unless specified otherwise in a monster’s description).
Disruption: Visible Light (normal or magical) and large heat sources prevent Infravision from functioning.

Parties carrying a Light in a dark environment usually cannot surprise others (see Surprise), because their presence is given away by the Light.

Falling from a height onto a hard surface inflicts 1d6 damage per 10′ fallen.

When travelling with a reliable guide, following a road, trail, or river, or heading towards an obvious landmark, there is no risk of getting lost. Otherwise, there is a chance of getting lost in the wilderness and at sea.
Chance: The chance of getting lost depends on the type of terrain being explored (see Wilderness Adventuring and Waterborne Adventuring).

If the party becomes lost, the referee will decide how far off course they are travelling (possibly at random).
Example: A party travelling through a swamp has become lost. The characters intend to head south, but the referee determines that they are actually heading southeast (45 degrees off course). After travelling 6 miles, the party decides to head southwest—they will then actually be headed south.
Rectifying: It may take some time for a lost party to realise that it is moving in the wrong direction.

Characters who go without food or water for a whole day or longer may begin to suffer penalties, at the referee’s discretion—for example, attack penalties, reduced movement rate, more frequent need to rest, or a slow loss of hit points.

Movement rate: Characters can swim at half their normal movement rate.
Who can swim: All characters can swim, unless there is an obvious reason why a character could not have learned.

The circumstances in which drowning is a risk—as well as the chance of drowning—are judged by the referee.
Example circumstances: Swimming in treacherous water conditions, swimming while wearing armour or carrying heavy or awkward items, fighting in water.
Example chances of drowning: A character swimming in rough waters while wearing heavy armour and carrying a heavy load may have a 99% probability of drowning. A character in the same waters but wearing Light armour and carrying a Light load may only have a 10% probability of drowning.

Besides the monsters specifically placed in certain regions of a dungeon or wilderness, PCs can randomly encounter monsters on the move between areas. These are known as wandering monsters.
See Dungeon Adventuring, Wilderness Adventuring, and Waterborne Adventuring for specific details.
Frequency: The referee should roll periodically to determine whether a wandering monster is encountered. The frequency of checks depends on the type of area being explored.
Chance: When a wandering monster check is made, the chance of a random encounter is usually 1-in-6. This chance can vary, depending on the type of area being explored (e.g. dungeon region or level, type of wilderness terrain).
Monster type: Each dungeon level or wilderness region has its own table of wandering monsters, which the referee rolls on when an encounter takes place.
Treasure: As wandering monsters are encountered on the move (not in their lairs), they seldom carry much treasure. This means that encounters with wandering monsters tend to present danger with little chance of reward.
Noise or Light: If the party is making a lot of noise or carrying bright Light sources in a dark environment, the referee may increase the chance of wandering monsters being encountered.
Hiding: If the party stays quietly for a long period in an out-of-the-way location, the referee should only make infrequent wandering monster checks.