A couple of puzzles to maybe try:

One I’ve done was they were in a room with 6 paintings of various lizards. On the back wall was were dials that when spun would give letters a-z. I set the code to “dragon” and I had a bunch of different reptile creatures I pulled from the MM. In the pictures there were a certain number of those animals with a plaque underneath detailing the painting (e.g., basilisks warming on rocks in a field). Now, the number of animals referred to a letter in the reptile’s name. And each picture had different reptiles (basilisk, kobold, lizard folk, etc). So, for example, 4 kobold gave you a “o”, 6 lizard folk gives you a “d”, and 2 basilisks give you an “a”.

When the players figured out the combos and input the answer in the dials they would hear a click noting they placed the right letter in the right place and when the word was spelled out a mechanism began to work and a secret door opened to another room and the dials reset for anyone else who would stumble upon that room.

Another one I was going to do was a variation on the fox, chicken, grain puzzle. In this they would be tracking down a crazy druid who went rogue and this puzzle would help get them closer to his lair. I did mine with hawk, frog, fly and a small boat has to cross the canal and they place these idols on the posts. If they were wrong then the idols would reset and some weak nature golems would attack.