Ideas with Redstone

A stack of boxes connected by funnels. To do this, a row of redstone lamps shows how many boxes are filled. Due to the large crate space, this is mainly suitable for paving stone or soil.

The trap is activated as soon as someone removes a block (here diamond).
The picture shows a cross section so you can see the inner workings. Normally, the floor around the diamond block is naturally flat.
The trap is based on the fact that you can set levers on block bottoms.

A little redstone circuit that causes the time to automatically reset to morning when darkness falls.
Attention! Since 1.6, you can also change the sun with the command /gamerule DoDaylightCycle 1 stop.

You throw an item or block into the hopper and get another item in return.

A button behind a pane of glass. Pressing the button opens a hatch in the ceiling from which water runs, the Redstone torch flashes and you hear an alarm sound.

A room without any noticeable things, which is converted into a room with a pool at the push of a button. Another push of a button causes the pool to disappear again without a trace.

There is only one correct zigzag way to the exit. When entering a wrong pressure plate, the door closes and you have to run back to the entrance for the exit to open again.

An invisible dispenser as this is hidden behind the wall. In the picture above I used the wall open and glass so you can see better how it works. The dispenser can be used well to poison players with throwing potions. But other items are also possible.

A secret passage which is completely invisible when closed and can be opened by a lever.

A relatively large code lock (about 30x20x10). It has little practical use, but is good for learning about Redstone.