One of the Underground Chambers also holds a Mountain Troll, but it has already been knocked out by the time Harry, Ron and Hermione reach it.
From the Story
"Mountain trolls are massive, unintelligent creatures. They tower over humans (Harry and his friends meet one that is twelve feet tall), with overly long arms and short legs that are thick as tree trunks. They have dull, grey skin, lumpy bodies, and small heads, and give off an odour like old laundry and unclean toilets."