Replaces Ayleid Ruin exterior meshes, sealing up the open sides which exist in inconvenient places (an open-sided mesh is one where you can see through it as if a bit was missing, because a bit IS missing)

When Bethesda created their mesh tilesets, they designed the joinable parts (where one mesh fits against another mesh) to be joined in very specific combinations, often leaving open sides at the places where two meshes are expected to be joined together, the assumption being that the meshes will only be used in the expected manner and so the open sides will all be neatly covered up.
Modders don't do the expected. Modders do what THEY want to do, and when that doesn't work, they find ways to MAKE it work. With open sided meshes, that means finding something else which doesn't really fit but will have to do to cover the hole up. And if THAT doesn't work either, well sod it, it looks cool from almost every other angle maybe no one will notice that from this side there's a big hole through to the other side... that's modding!

Well now all those openings in the side of the exterior Ayleid Ruin tileset have been sealed up, covering the holes with broken brickwork. Now you can use more combinations of the tilesets, you can place the blocks on their sides or upside down and they still look like blocks, you can have the Malada Tower mesh protruding slightly from the top of a cliff and no one below can see up its skirts (that's a metaphor, it doesn't have a skirt, but you get the idea). The crossbeam can be placed to stick out from the side of one structure, and it does NOT need to then hit the side of another structure to hide that it's just an empty tube, it can be a broken-off crossbeam that goes nowhere (maybe there's another bit lying on the ground now too). I could go on, but it would be easier if you just gave it a go.

Usage:
As a Mesh Replacer - if you use a lot of mods, there's a high chance that some of them already contain Ayleid Ruin exteriors, and have placed some things so that they have open sides clearly visible - one example is Unique Landscapes: The Eastern Peaks which uses a lot of Ayleid Ruins, and many of those pieces have clearly visible open sides. Even if you don't use ANY mods at all, Bethesda themselves have placed the odd Ayleid Ruin exterior mesh in the wrong place/at the wrong angle, leaving open sides, so it's useful to anyone, whatever mods you do or do not use.
As a Modder Resource - you can ensure that everyone using your mod will have Ayleid Ruin exteriors with no open sides visible, and won't have to keep finding clever ways to cover those open sides up.