Halaster's Scrying Cage(Expedition to Undermountain, p. 219)
Level: Sorcerer 9, Wizard 9,
Components: V, S, M,
Casting Time: 10 minutes
Range: Close (25 feet + 5 ft./2 levels)
Area: One 10 cubic ft./level
Saving Throw: None
Spell Resistance: No
This spell modifies the functioning of all divination spells and spell-like abilities into, out of, and within its area of effect, and it bars the functioning of all divination (scrying) spells into, out of, and within its area of effect.
If the spell is cast in an area adjoining or overlapping another scrying cage, the effects of both spells merge to create a single Scrying cage. Undermountain, the greatest dungeon of Faerûn, is believed to have been enclosed within the largest scrying cage in existence in the Realms by means of this combinatorical effect.
Effectively, this prevents the use of spells and spell-like abilities from the scrying subschool magic to scry within, into, or out of the warded area. It also prevents the use of spells or spell-like abilities from the divination school to peer through solid barriers, such as walls, doors, floors, or ceilings. Sending such spells through keyholes and the like does work.
When this spell is cast within, into, or out of a scrying cage, divination (scrying) spells simply fail to work and the spell is wasted. Other divination spells cannot bypass any continous physical barrier, such as a wall, ceiling or floor. Such spells can pass through any aperture, even one as small as a keyhole.
Material Component: Diamond dust worth 1,000 gp.