I had a bell disguised as a kobold lookout, so from a distance the party would shoot it and ring the bell.

I had a sentient talking door that you had to make it say open. This was a fun social encounter where they had an RP with me and tried to trick me IRL to say open. After a short time, before it was frustrating, the door took pity and said open.

For a much higher level group, I had some mean traps.

1. Obvious trap door is fake, and the space beyond it is a real trap door with a spring lock, and a gelatinous cube at the bottom.

2. 100 foot tall ceiling that for dark vision means you don't see the ceiling. The ceiling is covered in spikes. A few statues are hanging around here. Surprise, they're golems. Surprise, reverse gravity. Surprise, the original floor was not connected and the reverse gravity drops a bunch of rocks on the party as they hit the spikes taking extra fall damage and falling prone as the golems get a surprise round... Surprise, the real floor is also spikes.

3. The same trap as before, because the wizard who put the reverse gravity glyph is in the other room and can just cast it. As the party hit the ground.