The following are aspects of an environment which, while not always harmful, reflect an aspect of the locale. For example, extremely hot weather in the tropics, or darkness at night.
Unless a character is immune or resistant to cold damage, being exposed to cold weather has a risk for those in it. An unprotected character in a cold environment (below 40 degrees Fahrenheit) takes 1 point of ice damage bypassing Soak per round if they are hit by an attack to Bodily Defense (2k2 Attack, +1k1 for every minute unprotected in the cold). The ice damage is nonlethal, however if it brings the sufferer of the ice damage to 0 HP due to the nonlethal damage, the target henceforth takes lethal ice damage and will die. They are rendered unconscious when brought to -1 HP due to the nonlethal ice damage.
An unprotected character in a freezing environment (below -20 degrees Fahrenheit) instantly begins taking 3 lethal ice damage bypassing Soak per minute unless the attack to Bodily Defense (6k4 Attack, +2k1 for every minute unprotected in the cold) fails, in which it deals 2 nonlethal ice damage bypassing Soak instead, using the cold environment above for 10 minutes in-game time.
A character walking on ice may only move in straight lines, however they gain a +1 square move speed while doing so. Alternatively they can move at half speed without moving in a straight line, however they gain no bonus to their move speed from the ice, or any outside effects.
Areas with no light or very minimal light are considered dark. Characters without Darkvision can only see 3 squares in front of them (or lower at the GM’s discretion) and characters with Darkvision can see up to how far their Darkvision reaches.
Total darkness means a character without Darkvision cannot see at all, and those with Darkvision have the effects of Darkvision cut in half.
Heat, such as that from an incredibly hot desert, deals nonlethal damage over time. Once a character has taken an amount of nonlethal damage from heat that it’d bring them to 0 HP, all further damage is lethal. Use the rules for a cold environment for heat rules, except hot conditions are 90 degrees Fahrenheit, and extreme heat is 140 degrees Fahrenheit and above. Fire damage is dealt instead of ice damage.
Any character can wade in calm water that isn’t over their head, no checks required. Similarly, swimming in calm water over their head only requires a DC 10 Acrobatics check. Trained swimmers can wade in said calm water over their head with no check required. Armor and/or being encumbered prevents the ability to wade.
By contrast, fast-moving water is much more dangerous. Characters must make a DC 15 Acrobatics check to avoid going under. On a failed check, the character takes 1 points of nonlethal water damage bypassing Soak per round (+1 lethal bludgeoning damage bypassing Soak if flowing over rocks and cascades).
Very deep water is not only generally pitch black, posing a navigational hazard, but worse, deals 3 water damage bypassing Soak per 20 sq. the character is below the surface due to the water pressure. Very cold water deals 1 point of nonlethal ice damage due to hypothermia per minute of exposure.