The random summoning altars that appear in various areas. When you pass the check, it tells you that your theme has been changed to the theme of the altar - yet it doesn't change in actuality. It also doesn't give you the option of accepting the change in theme, either.
Related: the large book found in a some quests including Kant's Realm and at the end of A Most Curious Tome, the "Tome of Conjuration" also can't be interacted with.