On the lower right hand side entrance to the Baron pit you can place a ward in the wall "Shown Here": http://tinypic.com/view.php?pic=119ph7l&s=9#.V9HWhfkrLIU
Depending on the ward skin you use it can be completely invisible, i don't know if this is a serious issue at all but it's worth mentioning.
LappaDanielson1 votesWhat ward skin tho?
Zerenza1 votesThe drone one would probably be hard to see but that's not the point, that area of the baron pit shouldn't be able to be warded, you can't place wards in walls, it's a bug.
LappaDanielson1 votesbut.... what ward skin? did you place a ward to find this out or how did you come across this bug
Zerenza1 votesI accidentally placed a ward there while trying to place it next to the wall, because under normal circumstances it would fall right next to the wall and not inside of it, i also just checked in a custom game to make sure i wasn't just seeing things and you can actually slightly walk inside of it too.
Edit: Teemo can almost completely fit inside of it.