Sometimes the terrain is so difficult that you must clamber over it on hands and knees, rather than just carefully navigating it. Examples include junk-strewn rooms, vine-choked jungles, or waist-deep bogs. A creature wishing to move through such terrain must use a full-round action to move 5 feet. This is not treated as a 5-foot step and does provoke attacks of opportunity. Creatures attempting to move through impeded terrain cannot run or charge through such terrain, nor can they maintain any stances, including stealth.
Note that impeded terrain is not the same as blocked terrain, such as walls, locked doors or closed portcullises.
Some impeded terrain may allow an Acrobatics (if obstacles), Might (if climbing) or Movement (if swimming or flying) check to move more than 5 feet per full-round action, at the GM's discretion. As a general rule, however, spending a full round to move 5 feet does not require any sort of skill check.