Regular trains don’t run underground. Lots of opencast mines exist .

Basically all mines have an above ground terminal where whatever you mined is unloaded from your underground trains, lifts, haul trucks or whatever else onto storage piles, then loaded onto the actual long distance trains.

If the mine entry is up a mountain, then the trip down from that point will be a net energy producer regardless of anything else.

I wouldn’t be surprised if there are electrified railway lines doing the same. Regenerate large amounts of energy into the grid while descending loaded; consume a relatively small amount of energy to haul the empty train back uphill.

If you’re thinking of that CGI crane lifting concrete blocks, it’s unfortunately a really bad idea.

Pumped hydro stores energy by lifting weight uphill, instead. Water is basically the cheapest thing you can get per tonne, and is easy to contain and move.

To store useful amounts of energy using gravity, you need pretty large elevation differences and millions of tonnes of mass to move.