Huzzah! After a couple of hours browsing the official forums, I was lead to an external program which allows near-total world editing. Another hour after that to figure out the best way to do what I wanted, and I got to work.
One late night later, and it was all worth it. The town of Mystic Mountain is safe from being overrun by either Corruption or Hallow. There are still defensive upgrades, farms, and storage units to complete, and outside of carefully prepared barriers the dueling forces of light and dark run rampant. Still, underneath this mountain-turned-village-turned-fortress, life goes on.
Behold the main entrance! It used to be a much simpler affair; all the walls and bridges made of common, grassy dirt. As part of the preparations for hard mode, all exterior walls were replaced with much tougher dungeon brick. You may also see some defensive traps. More devious devices, including boulder traps, are in the works.
This is the primary crafting area. A cauldron for soup-making is elsewhere, but right here just about anything can be crafted. The Guide lives right below, always available to remind players of what exactly Coral or Mythril is used for. You can also see the living spaces for some other residents; the Dryad, the Tinkerer, and the Merchant.
One thing you may have noticed is the large amount of grassy dirt inside the halls. The grass provides natural carpeting...and I just think it looks nicer than stone and brick blocks everywhere
The current primary storage area. This place sufficed back when Mystic Mountain was little more than a hole in the ground, but with an ever-expanding amount of stuff to store it has rapidly become obsolete. A full warehouse is being planned deeper into the mountain, though transferring everything will likely be a chore.
Up here, at the peak of the mountain, is a secondary door/escape hatch. This place is inaccessible to any non-flying monsters, making it safe to leave unguarded - even in a Blood Moon.
The Shield Statue also rests here. It was the first statue discovered on this world, and has stood here ever since. The only time it came down was when the silver ore it rested upon was replaced by silver bricks.
Here we see the last pre-hard mode addition, the Statue Garden. It looks much nicer at night, with the soft glow of the lamps providing most of the light. Most unique statues go here, and benches provide a place to relax and enjoy the sunlight and artwork.
The rear entrance to the mountain. This one is much more of a gauntlet for invaders, though further refinements to the defenses are planned. This long bridge, abundance of pressure plates, and long firing lanes for the poison darts provide reasonable protection.
Here is the player character's living quarters. A full library addition is in the works, though more green brick is required before construction can commence. The Arms Dealer and Nurse live downstairs, and the Mechanic just kinda hangs out in the living room
The main hall, further storage, and rooms for both the Demolitionist and Clothier. A brewery is under construction underneath the Demo's room, and he's quite excited about it.
Built of magically-charged demonite bricks, the Wizard's room is the newest complete addition. Here, away from accidental guinea pigs, he experiments and practices his arcane talent. Shame he's going senile.
But for every triumph made by the denizens of Mystic Mountain, a tragedy occurred as well. Below the main entrance, under the watchful eye of the Dryad, lies the graveyard. This place has seen minimal upgrades or renovations, merely the addition of an Angel statue and a small shrine for visitors to leave offerings. With the world plunged into new struggles, I fear that this place too will need to be expanded.