Difficult Terrain

The setting of a typical fight contains difficult terrain. Every square of movement in difficult terrain costs 1 extra square. This rule is true even if multiple things in a space count as difficult terrain.

Low furniture, rubble, undergrowth, steep stairs, mud, sand, snow, and shallow bogs are examples of difficult terrain. The space of another creature -- whether hostile or not -- also counts as difficult terrain, unless the creature is Tiny (see Creature Size and Space).