Reward room

After you get the key from the key holder you finally get to reap your reward:

Reward Room	Description	Min. Depth	Frequency
Mixed Item Library	A room with a number of random items, guaranteed neutral or positive. You can only take one at a time.	1	30
Single Item Category Library	A room with a number of rings or staves, guaranteed positive. You can take only one at a time.	1	15
Apothocary or Archive	A room full of random potions or scrolls.	8	20
Pedestal	A room with one or two items on pedestals. You are allowed to take all the items. The room can contain: One weapon with a good runic effect. One suit of armour with a good runic effect. Two random Staves.	5	30
2 pedestals	Two pedestals with Scroll of Enchantment or Potion of Life on each.	10	30
Dungeon	Two allies chained up for the taking.	5	12
Kennel	Allies locked in cages in an open room; choose one or two to unlock and take with you.	5	30
Legendary Ally	Approach the altar with the orb to activate a portal and summon a legendary ally.	8	15
Vampire Lair	Allies locked in cages and chained in a hidden room with a vampire in a coffin; vampire has one cage key.	10	5
Outsourced item	A runic weapon or suit of armor inside a key holder instead of key.	5	20

Note that in every kind of reward room Rings and Wands will have their type (but not bonus) identified as soon as you see them, as of 1.7.1. Staves will have their type and maximum (but not current) number of charges identified. 

This article is related to version 1.7.2 and may be out of date.