dungeon construction: ordnance

By ordnance, I'm talking about the weapons of a dungeon, it's capacity to harm intruders and those who would otherwise raze it and destroy it's occupants. Defence is a major considerations of most dungeons (for those boltholes and fortresses it's the main one) and as the old saw says, a good defence is a strong offence. So those weapons become a key consideration for people who live there.

1. Armoury - If you've got an organised, militaristic group of monsters in the area, this is one of the things you'd expect to see. Apart from providing a mustering point in case of invasion by hostile forces, it also allows the owners to arm themselves according to need and if you're surrounded by enemies, conserving ammunition becomes a necessity; it is also a potential source of treasure to canny players.
   
2. Creatures - The monsters themselves may also be placed to do some serious damage to any intruders or interlopers. Guard creatures need not just provide alarm but also deter intruders by big, sharp teeth (and other features). While some creatures are effectively living deathtraps, others have different purposes (e.g. a gelatinous cube can be used as an effective septic tank) and just also kill things as an aside.
   
3. Environment - Large pools of lava needn't just provide illumination and hot water on demand. They can also roast anyone intruding into them. Having already touched on the dungeon environment, consider what lethal environments can be found there.
   
   
   • Ice caves can include crevasses, slippery slopes, snow drifts to slow down movement, glare from bright ice sheets and clouds of stinging ice-crystals borne on chill winds.
   • Lava beds can include jets of burning gas, pyroclastic bombs (large, heated rocks fired from inside the bed) and clouds of choking ash as well as poisonous gases.
   • Waterlogged dungeons can include sudden undertows, slippery mud or algae, tainted water (just don't swallow) and of course, aquatic monsters.
     
   
   
4. Traps - The purpose behind the trap can be many and varied, ranging from deterrent to buying time, to sealing off areas to outright death.
   
   
   • Deterrents can be as simple as a loud flashbang made by alchemical re-agents (with very little damage indeed) to a corridor filled with thread that if broken or snagged release a crossbow bolt in that direction (the threads feed through the walls back to a eyelet under a repeating crossbow).
     
   • Buying time can be done through slowing movement by a giant spider pinata filled with centipedes and caltrops on the ceiling (the pinata will move and dare the players keep moving under it?), pouring boiling oil down a stairwell or a rolling rock trap (which they have to let aside).
     
   • Sealing off areas enables you to control the movement of your enemies, whether this is by rotating or sliding walls or by controlled rockslides and portcullis traps.
     
   • Outright death - The poison needle in the chest is one way of doing this, as is the chute dumping the victim into a lava bed.
     

You needn't work out exactly to the letter how much damage the whole thing will inflict on the characters. Keep in mind the purpose and intent of the dungeon and assign ordnance by those categories and the abilities of the architect and occupants. An ogre may not be smart enough to restock the arrow trap but can certainly pull the rope to hoist up the piledriver trap again.