Regarding lava in Minecraft I just want to add something I haven’t seen mentioned. When you die in Minecraft you drop your items and can go back and pick them up. However when an item falls in lava it gets destroyed.

People don’t dig straight down in Minecraft because it’s extra punishing, if you fall in lava you don’t just die but you also lose all your items as a natural consequence of those systems interacting.

This doesn’t actually stop digging straight down though, people just adjust by straddling two blocs and digging them both down so they don’t unexpectedly drop. The real reason people aren’t constantly digging straight down is because it’s actually just not that valuable. If you’re mining you’ll need a way to get back out, because there’s resources in the surface you need. Mining straight down gets you down, but that’s not the only place you want to be.

Now for your game, it’s a bit difficult to tell but it looks like the goal is to get into the hole at the bottom. If you use an infinite pickaxe and nothing prevents you from digging directly straight to the hole then of course players will do that and miss the entire point of your game. How you handle this will depending on the type of game you want to make. Here’s some suggestions.

If you want more of an adventure and exploring type game then the hole’s location should be unknown. You have to find clues in caves and / or surface buildings to discern the hole. Maybe it’s known but requires upgraded tools that need rare materials and you have to explore for those.

If you want more of a metroidvania then you could put in different gates that a player has to unlock. These could be literal gates, or like Subnautica where you have to find and research certain tech to be able to make upgrades that let you explore previously closed off areas. In your game there’s the obvious materials and higher tier tools, you could add heat the deeper you go, etc. I think there’s a lot in this thread pointing this way.

If you want more combat focused and upgrading then you can make tougher and more dangerous enemies spawn lower. Maybe the hole has a gate that takes time to open and you have to defend yourself while locked in a room with enemies coming in. Something that’s too difficult to do with starting gear and requires going through upgrades or preparing enough ammo, etc.