Almost all terrains use a heightmap followed by individual rock/cliff objects to create steep slopes. This terrain shown could all just be a static mesh that was made in a modeling tool or heightmapped.

You could go into blender and sculpt a simple map and then go to turbosquid or so and probably buy some textured cliffs and plop them where you have really steep terrain.

Almost all terrains use a heightmap followed by individual rock/cliff objects to create steep slopes.

I wouldn't go that far. Plenty of games use techniques other than heightmaps :)

The game in the images is shadow of the colossus if I'm not mistaken. Games such as that, or Zelda or 3D mario games, etc would typically use 3D meshes for the terrain like you would for any other bit of environment art.

I don't know how they did it for SotC, but these days I imagine you'd make a very rough version in the hard surface modeller of your choice (max/maya/etc), then take it into something like ZBrush to sculpt it into a detailed bit of scenery, then remodel a somewhat detailed mesh over the top of the sculpt (retopologising), and then baking/transferring the high-detail scupt onto the new mesh as normal maps/etc.

You could also use a heightmap tool such as worldmachine to make the initial mesh, before you go to the hand-sculpting stage.

Using the "actual heightmap plus meshes for cliffs" workflow though, Star Wars Battlefront (2015) was pretty groundbreaking in this regard, where most of the cliffs/rocks were created using a photogrammetry workflow -- photograph a real rock from many angles, use PhotoScan/RealityCapture to convert to a high poly mesh, retopologize, transfer phototextures, cleanup textures to PBR maps. They also use a special shader on these rocks which blended into the heightmap-terrain shader wherever the rock intersected with the terrain. This made it look like the rocks smoothly blended into the terrain, instead of being a seperate mesh that was just stuck into the terrain. This actually made it seem like that the terrain itself wasn't just a heightmap, and fooled you into thinking that the terrain was a really big hand-sculpted mesh :)

Workflows on modeling / sculpting, texturing and so on?

there's a 6 part series on creating a realistic 3d nature scene from a photo in blender on youtube.

i think this is part 1

if this is the video i'm thinking of, they make the ground meshes, trees and grass models, all the textures, everything. yeah, i recognize it, this is the one.

then you just export to your format of choice, then import into the game (sometimes easier said than done).