I read a book 5-10 years ago where there were some wizards/monks/something similar where their success as wizards is limited to their concentration skills which they use to "build" their towers filled with books and artifacts.
The towers are imaginary, but still give them real power and the place where they store their knowledge.
This was an interesting idea, but I can't remember the author or the title or anything else.
Tondelo, one the the users of the Dark Dweomer in "Darkspell" by Katherine Kerr constructs "memory palaces" similar to what's been described in other answers (and in the current BBC TV series 'Sherlock'.)
In this sequel to her first novel, "Daggerspell", the author returns to the extraordinary world of Deverry and to the three enchanting characters whose poignant love transcends the boundaries of time and even death.
A minor but memorable feature of John Crowley's 1981 fantasy novel "Little, Big" is that one of the characters, Ariel Hawksquill, practices a form of "magic" whose chief feature is constructing buildings in the mind.
Ariel Hawksquill, greatest mage of this age of the world... Her one Great Art, and it was all she needed... The Art of Memory...
Little, Big - Book Three, Chapter IV
A description from the novel:
The Art of Memory, as it is described by ancient writers, is a method by which the Natural Memory we are born with can be improved tremendously, beyond recognition in fact. The ancients agreed that vivid pictures in a strict order were the most easily remembered. Therefore, in order to construct an Artificial Memory of great power, the first step (Quintillian and other authorities agree on this, though they diverge at other points) is to choose a Place: a temple, for instance, or a city street of shops and doorways, or the interior of a house—any place that has parts which occur in a regular order. This Place is committed to memory carefully and well, so well that the rememberer can scurry around it backwards, forwards, any which way at will. The next step is to create vivid symbols or images for the things one wishes to remember—the more shocking and highly-colored the better, according to the experts: a ravished nun, say, for the idea of Sacrilege, or a cloaked figure with a bomb for Revolution. These symbols are then cast onto the various parts of the memory Place, its doors, niches, forecourts, windows, closets, and other spaces; and then the rememberer has simply to go around his memory Place, in any order he wishes, and take from each spot the Thing which symbolizes the Notion which he wishes to remember. The more one wishes to remember, of course, the larger the house of memory must be; it usually ceases to be an actual place, as actual places tend to be too plain and incommodious, and becomes an imaginary place, as large and varied as the rememberer can make it. Wings can be added at will (and with practice); architectural styles can vary with the subject-matter they are meant to contain. There were even refinements of the system whereby not Notions but actual words were to be remembered by complex symbols, and finally individual letters: so that a collection of sickle, millstone, and hacksaw instantly brings the word God to mind when gathered from the appropriate mental nook. The whole process was immensely complicated and tedious and was for the most part rendered obsolete by the invention of the filing-cabinet.
Perhaps the Disciples of Aldur from The Belgariad/The Malloreon - they used the power of the Will and the Word. Sorry but I don't have any of the texts with me though, but from memory each sorcerer built his own tower with his mind.
