[Lazy_Perfectionist]

I've heard that both Cave City and Cave Fort battles are fought under the effect of darkness. I've also seen it in the short list of bugs.

Capital: Cave City
Default: Fortified City
Mountain: Cave Fort
Swamp: Swamp Fort
Forest: Forest Fortress
Tower weapons: 6x sling

Your capital is pretty well defended, but rather low on supplies. If you expect a siege, Pale One Soldiers are not a bad choice, as they don't consume supplies. Your admin is a measly 30, which means that it will usually be difficult to mass Ancient Ones.

Your Default Fortress of a Fortified City is exceptional. It's defense isn't ideal, but it is well supplied in case of sieges, and most importantly, it has 50% admin. Which means, build one of these in a strategic position to pump out the majority of your national troops. On second thought, your nationals aren't that special- a good independent selection works as well. When you build one of these, consider leaving out a temple and lab to save money.

In Mountain (NOT Border mountains) provinces the Cave Fort is available .It's admin and supply are measly, but its high defense means Pale One Soldiers can hold it for quite a long time against a larger force. Unfortunately, on random maps you will only see border provinces, at least at v. 3.08. It's on the expensive side though. I would NOT recommend making this your first fort. However... there are certain circumstances where its value jumps dramatically. A iron Mine, for instance. Or the Vaults Beneath (150 resources). Or some indies, or special site recruits. When that bug with auto darkness is fixed, if it isn't already, these will be extremely hard to take from you, barring a few nations.

Your Swamp Fort is abysmal- but cheap at 800 gold and 3 turns. It has absolutely 0 admin value. However, its not a bad place to put a library and temple, pumping out mages. If you want to double up your research early this is an option, albeit one that hamstrings troop production and vulnerable to attack. On the plus side, you could put one up next to a better fort, such as your capital, and it will hardly affect production.

Your Forest Fortress is not a bad choice. It's hardly ideal, but considering forests are high in resources and it goes up in four turns and 1000 gold, this is a decent production choice. If you haven't grabbed all the provinces in the area, its superior to a fortified city, but only by a small margin. I'd rank it above the Cave Fort, since it's somewhat less expensive, and goes up a turn earlier.

Next up, Strategy, Pretender Design, etc. Last, a discussion of artifacts and spells, advanced strategy, maybe?