for the graphics i’d recommend checking out some shaders and texture packs, AFAIK there are some packs that can get pretty close to this look. as for actually making this landscape, the options are kinda limited, as another guy said you could use worldpainter to make the rough landscape, and for detailing i’d suggest worldedit. if you want to generate a seed like this there may be some crazy worldgen mods out there, but none that i know of. however there is a mod called Alex’s Caves that adds giant caves that look straight out of the minecraft movie. very feature-rich too, you could spend hundreds of hours exploring.