If you have -100% magica cost in Alteration (posssible at lvl 100 enchanting -> 4 * -25%) and you cast the Telekinesis spell on a item you can open the map ant fast travel to a location. You will gain Alteration levels depending on how far you traveled, if ist a long distance Alteration will be lvl 100. Basically the game skipps time as a simulation of travelling but since you still cast Telekinesis it counts like casting it for the skipped time -> Leveling.
The Fandom Wiki has a description from the bug: [https://elderscrolls.fandom.com/wiki/Telekinesis_(Skyrim)]
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Telekinesis can be used to level alteration skill from 15 to 100 in minutes. Simply have -100% Alteration Cost (Secret of Arcana is a great alternative because it negates the cost of any spell), go outdoors, drop an item (preferably an unwanted item), use the spell in both hands, one after the other, so that dual casting is not in effect, but still using both hands to hold the object. Then initiate fast travel while still using the spell (the more distance traveled the higher it increases). The item will be left behind where you travel from, but may be found and recovered when you return to that location.
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I tested it on my modded save (no real game change mods) with the 4 enchanted gear -25% Alteration cost -> worked
And on a new save with just the USSEP (i used some commands to get the spell and tgm [toggle god mode] for the -100% magica cost) -> worked
Issue Data
Issue #29047: Alteration leveling (Spell Telekinesis) with fast Travel. [Instant level 15 ->100]