Throughout the dungeon are various objects with which your character can interact. These objects will become highlighted if you move the mouse pointer over them. If you click, your character will walk over to the object and activate it.
Doors seal off areas or rooms of the dungeon. None of the wicked creatures that roam the shallower dungeon levels can open them. This means that they can be very useful when retreating. However, if there are corpses in the way of the door, it cannot close. Just be aware that if you use the doorway as a bottleneck, you may not be able to close it off completely. Note that as the creatures get bigger, they usually get smarter, so some of the meaner creatures have the ability to open doors on their own.
Since the dungeon lies below a graveyard, every so often you will run across a sarcophagus, which contains someone's remains. Your character can investigate the contents of these tombs by activating them. Sometimes, you will find treasure among the effects of the deceased, or you may find it empty. Other times, however, the deceased will find you, in the form of a skeleton. Sarcophagi seem to only occur in the first four levels of the dungeon. Note also that the Skeleton King's lair is littered with unopenable sarcophagi.
Chests are littered throughout the dungeon, and are containers like sarcophagi. Unlike their giant cousins though, chests never contain beings. Small chests can hold up to one item apiece, regular chests hold up to two, and large chests can hold three items. Quite often, a chest will be completely empty.
Underneath the church, there are barrels for storage, sealed tightly. These are activated as normal, but instead of just opening them, the character attacks them, in an attempt to shatter the staves and release what is within. Unfortunately, sometimes the contents are explosive, and do damage. However, much of this damage can be avoided by ducking behind your shield. Also, some sick individual seems to have imprisoned victims within
certain barrels, victims which have now become revenge-hungry skeletons.
Traps are not really items you can interact with, in the same sense as the others, but they are closely related to chests and sarcophagi. Whenever you find one of these containers in the dungeon, there is a chance that it is trapped. If it is trapped, when you open it, an arrow will fly from an opening in the wall, aimed straight at you. Sometimes if you move out of the way fast enough, it will miss.
I know, it sounds macabre, but it's true! Perhaps the strangest type of container in Diablo is the decapitated corpse. In some dungeons, you will see them lying on the floor.
Libraries actually consist of two kinds of objects; the bookcase, and several library books. Each library book yields a single scroll, giving a one-shot spell ability. Sometimes, though, it turns out to be a thick book instead, which you can study to learn or enhance your spell ability. Bookcases always reveal one spellbook. Library books come in another form, called Skeleton Tomes. These are basically the same, except they occur near a
cabalistic ritual site, rather than a bookcase.
Tomes are huge books of lore, which are so heavy that you cannot even remove them from their pedestals. When activated, the tome opens, and you read its cryptic message. Some tomes will impart quests, in which case you can retrieve the text of the book from the quest screen. The other tomes are mainly just parts of the storyline which can also be read from the manual to the game.