Well as you already seem to realize the procedure is quite simple lots off copy paste and warping. I started with using a set off rocks in the form off a plain from a previous picture off mine (obviously I won’t make new stuff as lazy as i am ). So far im working in black and white so that i get, sortoff the same shading all over. Coloring it all later once I’m basically done with the picture by using overlay in layer optionschanging it from normal to overlay. With the "plains" I make out the for and structure off the cave by using the warp and perspective tools and simply taking my "plains" and making walls roof and floor with them. And then behind that the exact same thing but obviusly smaller so you get the illusion off distance or space. I probably suck at explaining things, get to carried away ^^ but i hope it helped. But the procedure is simple and fast which is what is nice about these kind off pictures .
yeah now i see. really cool use of those tools tho! I think its nice starting point to get some textures in those quite "flat", plane little spaces to individualize them a bit more (like darker "wrinkels"/scars or highlighted edges, that disappear more and more as they go into distance). Thanks for sharing this sir! Cheers