Let say we have a character with simple walk animation cycle which we looping, so our character constantly walk somewhere.
What if the floor have some slope, some little holes in the ground and so on.
Can we procedurally place character foot to the ground without manual ofsetting foot bones eact frame?
If you search for: blender walk on terrain then you see an answer from 2013 here on BA… or something newer else where 
Edit: (here not her 
) Don’t wanna be offending but yes it is posssible… happy blending.
I saw this. Its a basic and naive approach. Can work fine for distant shots.
I was meaning something like this:
Notice how “leg” on the right takes ground slope into account.
Its more or less basic so called “Foot IK” or “Foot IK placing” or just “Foot placing” technique which widely used novadays in video games so characters realistically walk in uneven surfaces (more or less).
But its require a line tracing (tracing line in 3d space, not like when you trace an image) and it looks like blender doesnt have such stuff which makes sense cause its not an game engine.
So maybe there some other solutions more commonly used in rigging/animation world which i just doesnt know.
The reference to 2013 was more something about: you can find anything if you are ready to dig deep enough .
I don’t know myself in detail for characters in not game engine blender but i know about some vehicle rigs ( for example quick search https://www.blendernation.com/2020/11/20/car-rig-pro-update-2-1-adds-suspension-types/) and i always thought that the Object Contraint: Shrinkwrap could be nice to put the foot on the ground so to speak. Of course this has to be done to maybe two or better three control bones to get the correct slant in x and y axis (if z is for height) which then control the food rig (and of course this has to be done with inverse-IK)… But didn’t get into this yet…
Okay, … interesting and was digging myself a little bit: indeed there seems to be not much about it. I found something for a stick figure with 2.7 (Walking along a path… but with height): https://www.youtube.com/watch?v=-5sY0CBV46w and some thng fro 2.8 “barely understandable” an not a real solution https://www.youtube.com/watch?v=6G61gZyo8D0
I think you have to dig through all this character walk cycles on path tuts to find something which really use a 3D-curve and not only follow this path in an upright position but also gets the slope into account… in retro perspective i remember all tuts i saw are going to finetune the feed on the surface (so no sliding is involved) but barely some terrain (maybe search word walk cycle on steps… or this gives you just bla bla in x easy steps)…
But there is so much about different actions while colliding with different objects and no much about slopped walk animations… 
i’m curious what this will end in.
Edit: 22 min later:
I think this is nice: Pierrick Picaut: Advanced ground matching run cycle tutorial in Blender 14 Oct 2020 but he also gets into the problem of sliding feet when the speed mismatches… but have a look at Wiresoul Studio: Blender Quick Tip WALK ALONG THE PATH Jun 2020 here is an object following a path and the walk cycle is connected to the object… seems to work better (expect upside down… you)