A long open pit filled with sharp stakes. There is a rope in the ceiling (with a weight at the end) the kobolds use to swing over the pit. The rope is coated in green slime (made from flour and colorant). The kobolds trust that they can use the rope for strategic movement and that adventurers dare not follow.

An ajar door has a pail of rocks resting on it. The kobolds can squeeze through the opening without causing the bucket to fall. The rocks deal 1d4 damage, half if you wear a helmet.

A long puddle with biolumencesnt sludge.  Its dark if undisturbed if the players walk through it gets agitated starts glowing and leaves glowing foot prints.

A good old pit trap!
...with a locking grate that falls across the middle of the shaft on a slight delay after the floor drops away.
...and arrow slits or kobold sally ports at the bottom of the pit, as well as murder holes or arrow slits at the top where the rest of the party is.

A heavy portcullis that drops across a narrow passage, splitting the party.  Probably manually triggered by the kobolds, rather than relying on a trap trigger, to get the timing right.  Flaming oil out of murder holes to encourage the party to split up rather than hang around there and lift/break the portcullis.

Scything blade traps set just above head height for a kobold.  Even better in a room where the kobolds make a stand in melee.

A drowning chamber, of Dwarf Fortress fame.  A long passage, lower than the rest of the complex, locked at both ends by grates or portcullises when an enemy reaches the middle, flooded with water from a cistern/chamber somewhere above.  Very long reload time for water to be pumped back up, only used once per dungeon invasion.

Not a trap, but de rigueur for lairs where kobolds have had time to work: secondary passages added by the kobolds, only large enough for a kobold to move through at a crouch or crawl.  Anyone else is going to have to belly-crawl, and possibly remove armor.  Ideally their hold-out lair will only be accessible via these, though they may have repurposed a larger room they've blocked off somehow rather than mining it out of solid rock.  Entrances crudely disguised by paper mache "boulders".

Not a trap:  some kind of venomous animals, such as scorpions or giant centipedes, tied to the ends of long poles and thrust at enemies to sting them.  Even if it only works as intended half the time, save or die, or even save or to sick to fight, makes it worth it against heroic enemies.

We also had a room with a dirt floor, which was full of deadly giant worms that were sensitive to anyone walking on the floor.

Hmm you might find this helpful: http://www.drivethrurpg.com/product/240834/Traps-Toolkit

How magical and/or steampunk are your kobolds? That informs much of their trap making. AKA, are they great trap engineers capable of feats of physics or are they somehow primally in touch with the Underworld?

Also, if the kobolds live there, they must be able to traverse the area safely, thus making traps based on non-kobold attributes such as height, weight, lack of darkvision, etc.

As kobolds are nasty bastards, but low HD and thus usually lacking great treasure, what is your motivation for the PCs? I've gone with the kobolds accidentally stole a bauble of far greater value than the owners knew, or of course, they stole some babies.

Quote from: jeff37923;1035603One of the traps I've decided to use is a knotted rope suspended from the ceiling. If any of the adventurers pull on the rope, it yanks out the keystone and collapses the ceiling.

It's a classic and works like a charm.

I've even required them to make a STR check. Just touching or tugging the rope won't do. You gotta put some effort into getting this trap to fall on your head!

Quote from: Spinachcat;1037186How magical and/or steampunk are your kobolds? That informs much of their trap making. AKA, are they great trap engineers capable of feats of physics or are they somehow primally in touch with the Underworld?

Also, if the kobolds live there, they must be able to traverse the area safely, thus making traps based on non-kobold attributes such as height, weight, lack of darkvision, etc.

Mainly set up to take advantage of character's typical weight. My pit traps are covered with thatch and dirt strong enough to hold a kobold or a halfling running over them, but not anything else. So, a kobold or two sees the party and is seen by the party, which then runs like Hell right over the pit trap, thus leading the PCs to their doom.

My kobolds are only partially steampunk. No lightning guns, but they can divert the smoke pipe from their smelter into a giant killer bee nest to smoke them out towards the PCs. I want to go for simple, but clever.

Quote from: Spinachcat;1037186As kobolds are nasty bastards, but low HD and thus usually lacking great treasure, what is your motivation for the PCs? I've gone with the kobolds accidentally stole a bauble of far greater value than the owners knew, or of course, they stole some babies.

The PCs will be searching for three stolen magic items which their patron wizard needs for a secret project. Clues will lead the PCs to the kobold tribe lair.

Kobolds stealing babies will be later, when I want the PCs to meet Tucker's kobolds.

"Simple, but clever" offers lots of room for creativity.

I like the kobolds having pets. Spiders are good choice since they won't set off traps. They also give reasons for kobolds having poisoned darts. I'd even allow the Druid or Ranger to identify the poison ichor as giant spider venom. Maybe even a phase spider pet for the kobold king. I'd even fudge and allow the kobold king to ride his phase spider and phase along with his mount.

Personally, the most vexing traps I find are stuff like the somethings that isolate one or more party members from the rest. I'm brutal as a DM. I let my players know that if you go into a lair of evil beings with the intent to slay them, they're gonna go medieval on your ass. It's not me. It's the vile nasties being vile and nasty.

I will drop a wall on the party, catching the least dextrous on the wrong side while sliding open the secret door for a nasty monster. Then PCs are fighting to help their friend who is getting butchered. Sometimes, they make it in time. Sometimes, they do not. Often, I will have foes show up for the other side of the wall as well. In general, I like the walls to allow at least sound to be heard. Portcullis are a fave. Cheap, strong, you might shoot some arrows through, feels possible to break through, feels "more fair" than a solid wall to some players, but gets the job done all the same.

[video]https://i.imgur.com/PSRtKp5.mp4[/youtube]

Depending on how far you want to go, the Grimtooth's Traps book series has a lot of ideas from the inconvenient to the ridiculously deadly.

Quote from: jeff37923;1037195My kobolds are only partially steampunk. No lightning guns, but they can divert the smoke pipe from their smelter into a giant killer bee nest to smoke them out towards the PCs. I want to go for simple, but clever.

Smoke causes bees to become passive and to huddle in their nest, smoking them out doesn't work.

One of my favorites is a pit trap that drops the characters onto poison spikes. A second trap door in the ceiling above opens to drop a Gelatinous Cube on the group.

Pits full of snakes are always good.

Couple ideas in here.  I guess one question is whether you want to keep 10' corridors, or go small.  I normally like keeping it easy and going with convention, but if there's any monster that's going to take advantage of small tunnels it's kobolds.

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Quote from: Dave R;1038588Couple ideas in here.  I guess one question is whether you want to keep 10' corridors, or go small.  I normally like keeping it easy and going with convention, but if there's any monster that's going to take advantage of small tunnels it's kobolds.

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I've seen this before. I have to wonder how much of this is really accurate, or if it was like, one-time things that someone saw, or just rampant speculation. Or maybe propaganda.