The Book of Hidden Dimensions

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There are many spells that are beyond the standard spells of the magical colleges, and they come from many sources. The Alphatian wizard Nebulon lived and worked over a century ago in the city of Shiell and he studied non-Euclidian geometry - impossible spaces and shapes. He wrote of his findings and new spells in a book, the Book of Hidden Dimensions. His students and apprentices made several copies of this and at least one of these copies found itself on the Floating City of Aalthir. 

The book itself contains quite a lot of mathematical theory and equations that non-wizards probably would never understand and even most wizards would find it difficult to wrap their heads around the concepts Nebulon tried to explain. Note that generally speaking Nebulon was interested in altering and manipulating dimensions not the Planes of existence so spells that involve the planes (such as Gate and Contact Other Plane) are not addressed. Nebulon himself modified some spells to make use of extra dimensions rather than planes of existence, such as his version of Leomund's Secret Chest. 

There is also a section on magic items that caught Nebulon's attention, including several pages on how to create a Bag of Holding and something known as a Portable Hole. 

The main attraction of the Book of Hidden Dimensions is the collection of spells in the second half. Some of these are well-established, others have been borrowed from other worlds while a few are of Nebulon's own making. The spells include:

• Haste (3rd level)
• Slow (3rd level)
• Dimension Door (4th level)
• Teleport (5th level)
• Teleport Any Object (7th level, Companion Rules, doubles as Teleport Without Error)
• Magic Door (7th level, Companion Rules)
• Summon Object (7th level, Companion Rules)
• Timestop (9th level, Rules Cyclopedia)

All of these are established spells that many wizards in Alphatia and beyond are at least aware of and usually have access to. There are also two modified versions of existing spells that suited Nebulon's sensibilities:

Passwall (5th level spell). This modified version does not actually affect the wall, but creates two connected dimensional portals on either side of the wall, so rather than making the wall section disappear, it simply creates an interdimensional shortcut to bypass the wall. 

Maze (8th level spell, Companion Rules). This modified version of the Maze spell does not use the Astral Plane as the usual version does but uses a convoluted pocket dimension that the trapped creature must find its way out of. While the creature is trapped in the pocket dimension, other people observe a vertical shimmering line where the target was when they were hit by the spell. On escaping the maze the target creature emerges from this shimmering line which then promptly closes up. 

 Then there are spells that Nebulon has acquired from other worlds and modified to suit his tastes:

• Deeppockets (2nd level Wizard spell, 2E AD&D PHB)
  Range: Touch
  Duration: 12 hours + 1 hour per caster level
  Area of Effect: 1 Garment
  This spell allows the caster to enchant a specially prepared robe or coat so as to hold far more in its pockets than it normally could. A finely sewn gown, robe or coat of high quality material with unusually large pockets is required. The spell is cast on the garment and its pockets become extradimensional spaces similar to Bags of Holding. The garment can hold a total of 100lb/1000cn weight without any noticable change in wearer's encumbrance or shape (i.e. the extradimensional space negates both weight and volume of anything in the enchanted pockets).Any items placed in it must be able to fit into the pocket slits (maximum 1ft x 1ft in any two dimensions). If at the end of the spell's duration there are items still in the pockets, they are dumped onto the ground next to the caster as the spell expires. The garment is reusable.  
• Rope Trick (2nd level MU spell, 1E AD&D PHB)
  Range: Touch
  Duration: 2 turns/level
  Area of Effect: Special
  When this spell is cast upon a piece of rope from 5' to 30' long, one end of the rope rises up until the whole hangs perpendicular as if affixed at the upper end. The upper end is in fact fastened to an extradimenional space. The spellcaster and up to seven others can climb up the rope and disappear into this space of safety where no creature can find them. The rope can be taken into the extradimensional space if fewer than 8 persons have climbed into the space, otherwise it stays hanging in the air. Spells cannot be cast across the dimensional interface, nor can area effects cross it. Those in the extradimenional space can see out of it as if there is a 3' x 5' window centred on the rope. The persons in the extradimensional space must climb down prior to the end of the spell or they are dropped from the height at which they entered the space. The rope can be climbed by only one person at  a time. Note that the rope trick spell enables climbers to reach a normal place if they do not climb all the way to the extradimensional space. Also not that creating or taking extradimensiona paces into an existing extradimensional space is hazardous.  
• Leomund's Secret Chest (5th level MU spell, 1E AD&D PHB, modified from original)
  Range: Special
  Duration: 60 days
  Area of Effect: 1 chest about 2' x 3' x 3'
  This spell enables a specially constructed chest to be hidden within an extradimensional space (in the original this was hidden in the Ethereal Plane). The large chest must be exceptionally well crafted and expensive, constructed for the caster by master craftsmen - the cost of such a chest is never less than 5000gp. Once it is constructed the magic user must have a tiny replica (of the same material and perfect in every detail) made so that the miniature appears to be a perfect copy. The chests themselves are nonmagical and may be fitted with locks, wards and so on as any normal chest. While touching the chest and holding the miniature, the caster chants the spell. This causes the large chest to vanish into the extradimensional space. The chest can contain one cubic foot of material per level of the magic user no matter what its apparent size. Living things make it 75% likely that the spell will fail so the chest is typically used for securing valuable spellbooks, magic items, gems etc. As long as the spellcaster has the small duplicate of the chst he can recall the large one from the extradimensional space whenever the chest is required. If the miniature of the chst is lost or destroyed there is no way, not even with a Wish spell, that the large chest can return. If the large chest is not retrieved before the spell duration elapses there is a cumulative chance of 5% per day beyond the end of the spell that the large chest is lost.     
• Duo Dimension (7th level MU spell, 1E AD&D PHB, modified from original to ignore references to the Astral Plane)
  Range: 0 (Caster only)
  Duration: 3 rounds + 1 round per level of caster
  Area of Effect: Caster only
  A dui-dimension spell cuases the caster to have only two dimensions - height and width but no depth. He is thus effectively invisible when turned sideways. This can only be detected by  True Seeing (as it is not the same as normal invisibility). In addition the caster can pass through the thinnest of spaces as long as these have the proper height - going between a door and its frame is a simple matter. The wiard can perform all actions normally. He can turn and become invisible, move  and appear again. The caster can cast other spells while in this state. Note that when turned the wizard cannot be affected by any form of attack but when visible he is subject to double the amount of damage for an attack, e.g. a dagger thrust would cause 2d4 damage if it struck a duo-dimensional wizard.  
• Morden's Magnificent Mansion (7th level Wizard spell, 2E AD&D PHB)
  Range: 10 yards
  Duration: 1 hour/level
  Area of Effect: 300sq ft/level
  By means of this spell the wizard conjures up an extradimensional dwelling, entrance to which can only be gained at a single point on the plane from which the spell was cast. From the entry point those creatures observing the area see only a faint shimmering in the air in an area 4' wide x 8' high The caster controls entry to the mansion and the portal is open or shut on his command. Once observers have passed beyond the entrance they beohold a magnificent foyer and numerous chambers beyond. The place is furnished and contains sufficinet food stuffs for a 9 course banquet for 12 people per level of the caster. There is also a staff of Unseen Servants obedient and ready to wait on those who enter. The atmosphere is fresh, clean and warm. Since the mansion can be entered only through its special portal, no outside conditions can affect the mansion or those inside. Rest and relaxation within the mansion is nromal but the food is not. It seems excellent and filling as long as one is within the palace. The food cannot be taken outside the mansion. Once guests are outside , however, the effects of the mansion's food disappear immediately, and if guests in the mansion have not eaten real food within a reasonable timespan, ravenous hunger strikes and the effects of fatigue and starvation apply as decided by the DM. 
• Phase Door (7th level MU spell, 1E AD&D PHB)
  Range: Touch
  Duration: 1 usage/2 levels
  Area of Effect: Special
  When this spell is cast the wizard attunes his body and a a section of wall is affected as if by a Passwall spell. The phase dorr is invisible to all creatures save the spellcaster, and only he can use the space or passage the spell creates, disappearing when the phase door is entered, and appearing when it is exited. If the caster desires, one other creature of man size or less can be taken through the door. This counts as two uses of the door. The door does not pass light, sound or spell effects, nor can the caster see through it without using it. Thus the spell can provide an escape route. The phase door lasts for one usage for every two levels of experience of the spellcaster. It can dispelled only by a casting of dispel magic from a higher level magic user. 

Finally there are a collection of spells created by Nebulon himself: 

Nebulon's Hideaway

Spell Level: 5
Duration: 1 hour per caster level
Range: 10'
Area of Effect: 20' x 20' x 20' (in another dimension)

This spell creates a temporary extradimensional space about 20' x 20' x 20' with a door that can be opened or closed by the caster, which can be placed against a wall or in the middle of the ground. When the door is closed, it is invisible and intangible - only a True Seeing spell will reveal it.  As the Hideaway is extradimensional, it ignores normal geometry so the area behind the portal in normal space is entirely unaffected. Characters can enter or leave the Hideaway as often as needed (with the caster controling the door) for the spell's duration. Although empty and unfurnished, the Hideaway is kept at a steady room temperature making it a haven in hostile environments. As with Phase Door and Morden's Magnificent Mansion, spells cannot be cast into or out of the door nor can spell effects pass through. 

Nebulon's Permanent Chamber (Reversible)

Spell Level: 8
Duration: Permanent
Range: 10'
Area of Effect: Special

This improved version of Nebulon's Hideaway creates a permanent extradimensional space of up to 10' x 10' x 10' per level of the caster (so a 16th level magic user could create a chamber 40' x 40' x 10' (16000 cubic ft). The doorway to this extradimensional chamber is permanently open but it may be secured by mundane or other magical means. Each casting of this spell requires a component - a perfect cube of some precious gem such as sapphire, emerald or diamond worth 1000gp, which is consumed in the casting. The walls on the inside of the chamber take on the hue of the gemstone used. 

It is possible to use multiple castings to join several chambers together in the same extradimensional space, perhaps creating an entire extradimensional complex. There is also a reverse of this spell, Delete Chamber, which will destroy a chamber created by this spell - this and a Wish spell are the two only ways to actually destroy Nebulon's Permanent Chamber. Anything inanimate still inside a Chamber when it is deleted has a 50% chance of being dumped immediately where the door was (i.e expelled into the normal dimensions) or 50% chance of disappearing forever (expelled into other, far dimensions). Living things and other monsters are always dumped into normal dimensions (so deleting a Chamber is not a way to kill a creature).    

Nebulon's Joined Doorways

Spell Level: 6
Duration: 1 turn per caster level
Range: 60'
Area of Effect: 2 doorways 6' x 3' each

This spell allows two doorways up to 60' apart to be joined by an extradimensional connection. The two doorways must initially be mundane and must have been seen by the caster. The extradimensional connection cannot be created in the middle of an empty space - there must be a physical door frame or archway to anchor it. Once connected, stepping into one doorway means immediately stepping out of the other one. The doorways are two way and the spell itself does not offer any restriction of who can or cannot enter, though the caster can end the spell at will. This spell has a duration of 1 turn per caster but higher level magic users can use a Permanence spell on the first doorway once cast to make the spell effect permanent. This spell can be used as a prepared escape route or for magical burglaries. Since the distance between the doorways can be vertical, it can be a shortcut between levels of a dungeon or storeys of a building.

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