Couple people pointed out finding a Hallowed Knight with ?? (have to be higher level to see the level), but if you farm him you have a chance to spawn an Anointed Ogre also level 16. Will not post where to find them exactly, but they are in a room by a cliff. So if you do any form of damage to them, then get on a bike and push them off the cliff. You will get the kill registered and get the xp and glimmer. Also, with every spawn there is a chest that gives glimmer and an item.