What happens when you take out the blue wool from a desert pyramid?

Solution 1:

There is a deep pit with 4 chests (which contain various items: iron and gold ingots, diamonds, emeralds, bones...) and a pressure plate in the middle. Underneath the pressure plate are 9 blocks of TNT which explode after some time if you step on it.

The player in this screenshot is in the place of the removed blue wool block. One piece of sandstone at the bottom has been removed by me to show the TNT. The room is well lit because there is a hole in the ceiling right above the blue block.

You can easily avoid the pressure plate if you dig out one of the adjacent blocks to the blue one (note that now the pit will be much darker), but the fall is still quite deadly and takes 4 hearts.

And here is a video that demonstrates this: