Black, English, or Carpatian? Not that it really matters, the husk is a misery to get off (but Black is absolutely the most difficult,IMHO). We don't usually pile up the nuts.. too much chance of rotting the good insides, not mention a couple dozen squirrels and chipmunks who would think the pile was meant for their dinner. No matter how tempted, do NOT run over the nuts with your car. The shells will fly everywhere, endangering everything and everyone within reach.

A lot of folks soak the nuts, for how long seems to be a guess, usually overnight. Then encase yourself in old clothes (becuz they are going to be tossed when you are done), and wear safety glasses; get a hammer and a very firm, sturdy surface. DH uses a 4"-thick slab of wood that is about 15" across and slightly concave. He just whaps the hull, pieces fall off, and eventually there is the inner shell. I do a variation of that theme, but use a board with holes which are from 1 1/2" up to about 3" diameter. I bridge the board so the ends rest on cinder blocks. The hull is placed over a hole that looks about 1/2" smaller and *then* I go whap with a hammer. Most times, the hull comes off and the nut falls through the hole - sometimes after several whaps. If a chunk of hull sticks, I just repeat using a hole slightly bigger than the nut.

Link is on black walnuts. Once you learn to husk the blacks, everything else is easy. BTW, make or invest in a screw-type nutcracker... fastest way to get mostly halves of the nutmeats.

Here is a link that might be useful: re black walnut husking

I've got an easier, less messy way. Just 'roll' the nut beneath your booted foot on a firm, hard surface - this works best when they're green, but will also work on softer, blackened husks. Most of the time the vast majority of the husk material is almost completely removed - but wear gloves to pick up the freshly husked nuts, or you'll have stained fingers/hands.
If you pile the nuts or let the husks turn black & mushy, the pigment from the husk can penetrate the shell and discolor the nutmeat, also imparting an undesirable flavor, so it's best to husk them as soon as is possible after they drop.
Once you've removed the bulk of the husk, dump a bunch in a bucket of water and stir vigorously with a stick, pouring off the water & adding new until it comes off clear. Additionally, if any of your nuts float, they are probably incompletely filled 'blanks', and should be discarded.
Then, spread your clean nuts in a cool, dry place to cure for at least a couple of weeks - straight off the tree, they're not very tasty.
A nutcracker designed for use on black walnuts is great, but a sturdy bench-mounted vise will also work fine, albeit a bit slower. It helps to soak the nuts in a pan of hot water for an hour or two prior to a session of cracking - the shells will absorb enough moisture that they bend, buckle, and split, instead of 'exploding' when you reach 'critical pressure' - rewarding you with intact quarters/halves instead of tiny fragments. Nuts from different trees have differing cracking characteristics - some crack better end-to-end, others side-to-side; you have to play around a little bit to figure out what works best. With a good nutcracker or vise, a pair of diagonal wire-cutting pliers, and a nutpick, you should be able to get good nutmeats out of even the thickest-shelled wild-type black walnut out there.
Some of the 'improved' BW selections, like Emma Kay & Thomas Myers have thin shells, and kernel percentages in the range of 35-40%, compared to the typical 15% for most run-of-the-mill wild types.

Lucky P - Boots were never sufficient for smooshing the hulls off our blk walnuts, but maybe that method works best when the nuts are right off the tree?

Thanks for tip about soaking just before cracking - I'll try that.

yep. works great on fresh, green nuts right off the tree.

Other methods include dumping 'em in the grave driveway and driving over them for a few days - I still do that with some of mine; or running them through an old-fashioned hand-cranked cornsheller.
Some of my friends who do it on a larger scale have a small, motorized cement mixer that they dump theirs in, with some rocks and let it go for a while with the water running - nuts come out incredibly clean!