There is an exploit in Minecraft that every speedrunner knows of and it has been kept secret for over seven years.
If you are looking for something underground like a spawner or hidden base, there are ways to find it without using cheats or x-ray.
If you turn on View Bobbing from your game settings, your head will shake up and down when walking.
This same setting can be used for an exploit that speedrunners and all good Minecraft players use.
If you turn on View Bobbing and make an underground tunnel, you will be in third-person and be able to see through the blocks if you position your mouse correctly.
This trick can help you find hidden locations very easily and the exploit is often used in speedruns and challenges.