There is a cool X-Ray glitch (some people already know it) that when you push TNT or some other types of block into yourself (doesnt suffocate you) you can see caves and other things to look for. I find this pretty useful in servers. You should try it yourself! You need some redstone, 2 sticky pistons, and TNT or some other block. I have found many dungeons with this glitch. So its pretty useful!