This page is being considered for removal. The altars are now activated by a skull of the color of the floor you are on, and are only present in the adventure tower, so this information would be better placed on that page. As far as the hero special items, that chart would be better placed either on the avatars page or a separate page in the armory.
Some items found in the dungeons are Special Items that cannot be taken from the dungeon. These items can neither be dismantled nor equipped. What they actually do is trigger special encounters when brought to a certain space in the dungeon in which they are picked up.
The space to which you must bring the Special Item to trigger the encounter is not marked in any special way, and may be a space you have already travelled past before picking up the item. It may also be on another floor of the dungeon (verification needed).
Below is the list of known Special Items, along with the dungeons they are found in and encounters they trigger.