De Castellis Altissimis

[VoxRationis]

So it's fairly common to see fantasy art with implausibly tall castles, stretching many hundreds of feet into the air, constructed of a tight cluster of spires, often with little to no clearance between them. The first page of Part 1 of the fifth edition Player's Handbook of D&D is a good example of what I'm talking about. Dominion's cover art has a less preposterous one.

Leaving out, of course, the structural difficulties in extending castle architecture to such heights (by saying that either the stone is magically reinforced, or the construction is actually much less medieval than it looks, supported with girders of highly advanced metals, or the majority of the interior is some sort of projecting rock formation), has anyone ever included such a site in their games? Has anyone mapped out the vast interior of a castle of such size? What reasons have you put forth in your settings for why someone would invest so much in building so high? In short, what have you done to run with this concept?

[Tiadoppler]

I've used them (the metal girder construction with stone facing variant) as airship docks/full airship ports. Sort of the way the Empire State Building was (going to be) used. You need multiple spires for docking multiple ships simultaneously, while allowing them to drift with the wind direction without hitting each other. They have many bridges (covered and uncovered) in between the outer docking towers and the central hub to aid in moving passengers and cargo from ship to ship, or down to the surface level.

They can also be the source of a ground based "Kill-Sat". Think of a big, immobile magical laser weapons platform that relies on line of sight. The base of the castle (on top of a mountain) is heavily fortified and contains the power source, and there are several towers (containing the laser emitters) reaching up as high as possible to provide the weapon maximum range and field of fire. The smaller towers can be used to fire multiple, simultaneous lower-powered beams, and the highest, central tower is used for maximum single-target damage.

[Lapak]

One of the more reasonable non-airship purposes is one that people actually used towers for: prisoner storage. Particularly if the top is protected from magical intrusion or direct assault (anti-magic field covering the top, no windows and solid construction to prevent non-magical flyers from gaining access) a narrow, very tall tower with only one stair and multiple guard-stations located along that stair makes for about as secure a setup as you can reasonably hope for. Even if a rescue mission makes it in, reinforcements can potentially come on their heels and bottle them up.