With the cheating mod Julialy’s X-Ray, you can easily find all kinds of ore, as well as interesting places under the surface. It has three modes, for each of them you can assign a button in the control settings. The first mode removes all but valuable blocks, which will quickly find iron, gold, diamonds and other resources. The second mode removes even more textures, including leaves and much more. The third one was created specifically for finding caves and spawners.