10' Pit? No 100' Dragon
Traps are most often mechanical or magical things, but looking at it abstractly, traps are a challenge to overcome that is not really combat based. At some point I started using monsters as traps - monsters that are incredibly deadly and well beyond the capabilities of the players.
For example, a pack of adventurers skulking around a dungeon comes across a chamber they need to get through ... except there is a huge dragon in it. Fighting the dragon will almost certainly end in doom. If they spring the trap (waking the thing up) there will be consequences (damage/death/etc.) but disarming (laying down some additional magical sleep on the thing) or avoiding the trap (sneaking by) will reward the players by giving them more dungeon access, treasure, or what have you.
In my recent game, there was a huge demon trapped in a sarcophagus. It was described ominously, opening it has ominous results. It was obviously a "bad thing" ... but adventurers love danger and had to muck about with it. At this point the trap is set and the players are going to spring it ... and spring it they did! The next session the demon possessed and killed a character (not to mention caused massive damage to some others). The session after that the party went back to where the thing was and it not only caused holy hell with the party (another character dead) but they let it escape into the world ... which has consequences.
Some might call this a "no win" situation. I posit, however, that the warning signs were there and the previous experience with the trap/demon showed it was a deadly thing. Winning would have been avoiding or leaving the thing alone. Engaging the demon was devastating ... just as would be walking into a room with 100 swirling giant blades obviously coated in poison.
I don't use this trick/trap often as it would simply make the dungeons far too deadly, but having them lying about keeps players on their toes and keeps things interesting. In a game where combat is deadly and the focus is more on exploration and loot that fighting monsters, these encounters help set the perfect tone for my game.
Trap Monsters vs. Monsters as Traps
There are some classic trap monsters - mimics, lurker above, trapper, that sort of thing. These are not the same as monsters as traps. The encounter with them is a monster encounter, just disguised as something else ... these are more ticks than anything else. Monsters as traps are obvious ... trap monsters are not. Giving clues as to the situation are the same as giving clues to any monster encounter. Broken statues of terrified people mean there is some old school shit that turns you to stone around the area. There is something less satisfying about a treasure chest springing to life and trying to devour a character (making all future treasure chest encounters take 20 minutes instead of 30 seconds) than watching the players realize there is something well out of range and deciding to walk into it anyway.
Just some food for thought.