Make a stairway to heaven
- essentialy a stairway that springs up above a massive pool, as it turns in a spiral it is walled the entire way round by waterfalls, technicaly, you can do this with just 2 pump stacks if you think about it enought.
also: the pool must have no water source bar the initial filling up etc. therefore, if you screw up your rates theirs a grand chance of flooding the stair way into oblivion. -wich if you decide to make this into an entrance would be a great way of making a defence.
bonus points in a freezing biome.
bonus points if this stairway disects the caverns -all 3 layers- or runs around the entierty of the fortress as a massive pool etc.
another challange:
Water wall defence.
essentialy: 2 walls, the inner is 2 thick, the outer is 1, theirs only 1 tile between them. and at least 1 tile empty space between this wall and the outside. -magma sea or lava at bottom- The inner space must be floored every level, and have hatches/doorways linked to levers to allow controll of water in those sections, so that when toady implaments construction destroyers and diggers, when the wall is breached, the water can be diverted for repairs to be made after the seige is done.
what water you say? well: the top of this wall must come to a group of pumps that takes water from the bottom right to the top of the wall, ie from just above the magma sea to say +5 z levels. this floods the inner wall space so that when the outer wall is breached, it floods water out and pushes the invaders off of anything they used to bridge the gap outside the wall. -must also have sturdy roof made of walls, not floors, so any caveins are next to useless to cause- The pressure of the water pump forces any tunnel diggers to surface or die, as their entier diggings are flooded out.
The entrace must be ingeniously placed drawbridges -2 will be required at least- that does not break the wall of protective water untill sealed off via mechanisms and drained.
This Water Wall defence is good vs anything and everything bar flyers, so the top of the fortress must be a heavily fortified tower reaching into the sky.
The end result? you have a mega fortress with better defence than most.
The bonus points: do it with magma, and use an aquifyer as your internal source of water.
This turns it into the Magma wall defence.
Extra bonus points: permanent freezing biome with water. make it so that it only freezes once its pushed any future diggers to the surface etc.