Hello again guys. About a week/week and a half ago I posted a thread about needing help with basic dungeon-making and the messages and assistance I received was astounding. So, I'm asking for the community here to do me one more huge solid and help me out with how to design logic puzzles.
I've always loved puzzles in games and my players have all made it abundantly clear that they want a lot of these things. The only issue therein is the fact that I am absolute trash at making logic puzzles. I'm sure I could google some and slap them into the dungeon, but I was wondering how other DMs went about making original logic puzzles for their games?
Any insight on this matter is welcome. Thanks ahead of time to everyone who posts here.
I Google them, and then change all of the terms to medieval terminology to make it flow better. I'm trash at making original logic puzzles. Riddles are another story though 
Here's a puzzle I've used with two different groups with good results.
There are 4 chests with a sign above each. In front of this is a plaque with instructions for the puzzle.
The plaque with instructions: Four chests, each with a sign above them. Beware opening the wrong chest! One sign is true, the others are false.
Chest 1 sign: The treasure is under a false sign.
Chest 2 sign: There are at least two true signs.
Chest 3 sign: There are at least three true signs.
Chest 4 sign: The sign over chest 1 is true.
Solution: all 4 chests are trapped. If the instruction plaque is inspected, you will find it slides aside to reveal the treasure.
Reasoning:
The plaque with instructions states exactly one sign is true. Therefore the chest 2 and chest 3 signs are false.
If the chest 1 sign is true, so is the chest 4 sign. If the chest 1 sign is false, so is the chest 4 sign.
Therefore, the plaque seems to be lying. What to do?
If you consider the plaque to be one of the signs, then there are actually 5 signs. There are now two solutions consistent with the information given:
1 - The plaque is true and all of the chest signs are false. Since the chest 1 sign is false, the treasure must be under a true sign. The only true sign is the plaque.
2 - The plaque is false, and all of the chest signs are true. Since the chest 1 sign is true, the treasure must be under a false sign. The only false sign is the plaque.
Here's some examples of puzzles/encounters that I have used in my campaigns:
Lore puzzle
The players encounter a door with three large cylinders in it (with pictures of various important rulers) that can be rotated, along with three nameplates underneath them that can also be switched around. The nameplates do not contain names however, but popular quotes. The players need to match the right quote, with the correct ruler, and put them in the correct order (starting with the three founders). The answer to this puzzle is spread throughout the dungeon, where the players can find various tombs of important rulers, with their quotes written on the lid.
Moral choice puzzle
The players make their way through a maze of small rooms, each presenting the players with a tricky moral question. Each time they make a choice, they are teleported to the next room. This allows the players to see what choices their fellow party members make, and it allows them to think about the question as a group. The sum total of all their answers can have various effects on the outcome of the puzzle, at the DM's discretion.
The 12 keys (wizard only)
The wizard of the party is locked inside a room, with a magical door that is kept shud by six magical locks. In the room are about 12 keys, but the player needs only 6 to exit the room. Each key requires clever use of a spell (but there are multiple solutions, since there are so many spells). The player has not had time to pick the right spells in advance, so he'll have to make due with what ever spells he currently has memorized.
* One key is floating out of reach.
* One key is encased in solid ice.
* One key is deep underwater, at the bottom of a well.
* One key is invisible.
* One key is hidden inside a locked chest.
* One key is ethereal.
* One key is lying in a pool of what seems to be water, but this turns out to be concentrated acid.
* One key is lying in a magical fire.
* One key is behind a wall of force.
* One key is inside a cloud of magical darkness.
* One key is polymorphed into a useless object.
* One key is stuck inside the wall, surrounded by stone.
To solve this puzzle, the player will have to be clever with his spells. A dispell magic might work for some of these, but how many times can the wizard cast that spell? Because the number of spells that the wizard has memorized is a bit of an unknown, this scenario requires only six keys to complete, since some of them he may be unable to acquire.
The flooding room (fighter only)
The fighter of the party (could be a warrior, paladin, barbarian, or any class that is good in melee) is locked in a room, from which only one door offers escape. The door is locked, and requires a key. Unfortunately the room also contains three angry crocodile soldiers, one of which has the key attached to a ring on its nose. As the battle starts, the room slowly starts flooding with water. Will the player be able to get his hands on the key before he drowns?
The crododiles will of course have no problem with the fact that the room is flooding. If the player succeeds at a grapple, and a strength check, he may be able to remove the key with sheer strength without killing the crocodile soldier. But if he tries to run to the door, they will try to grapple him along the way. The DM will have to make sure that the three crododiles are a fair match for the player. This should be a winnable scenario, and the DM can decide just how fast the rooms floods.