I’m playing on one of the more recent experimental versions and for the life of me cannot figure out how to get dig downwards to work properly. I’ve done it on a previous version, but every time I try it now I get the message “Halfway down, the way down becomes blocked off.” Has anyone figured out a way to get this to work? I really don’t want to have to go rock hunting on the overworld, that usually leads to some fun with landmines.
you need a pickaxe or something to bust through the blockage with.
Landmine fields are pretty clearly marked nowadays. Don’t walk in the field between the signs.
You can’t dig down without using a pickaxe in the first place, so that doesn’t help any. 
Mine fields are indeed marked by those signs, but when you’re hunting for rocks at night time or in bad weather, you sometimes will end up slipping between the signs without seeing them. BOOM!
I’m hoping it was just a bug with that version, I’ll try it again on the most recent experimental and report back.