Cave exploration in Openworld: lava, oil and crystals under a round planet

What's in Openworld's caves?

Openworld is a voxel sandbox on a whole, round planet — walk straight and you come back to where you started — under a real sky with Moon phases and eclipses. On Mac (native Apple Silicon), Windows and Linux. And under that planet, the ground is not a backdrop: the game carves a real cave network into the first 200 m under the surface, then dresses it according to depth and to the climate up above.

Three families of caves share the underground:

• Tunnels you can follow for minutes: 2 to 9 m wide, flat floors, forks, rooms where they meet, entrances that open in the ground — and ravines.
• Winding tubes 2.5 to 4 m across that climb and dive at every angle: the ramps and shafts between the levels of the network.
• Caverns: halls 10 to 60 m wide, 45 to 95 m down, with domed ceilings and stone pillars thick at their foot.

What you find inside depends on the land above you. Four cave climates:

• Dripstone caves (the most common): calcite stalactites, stalagmites under them, columns where they meet, gravel and clay floors. Under hot deserts, crusts of saltpetre.
• Lush caves (humid, mild land above): carpets of moss, curtains of vines, glowing mushrooms.
• Frozen caves (cold land above): ice floors and icicles of packed ice.
• Deep caves (from 68 m under sea level): basalt floors veined with magma rock, clusters of glowing crystals.

Under the grass
A few meters of soil, then rock — and already the dark specks of coal and pale grains of iron.

A lava lake
It breathes and lights the walls orange. A magma golem patrols its shore.Lava lights 12 m around it: you'll see it coming.

Click them
Bats, spiders, golems… and a knight holding off a troll. Hit a creature three times and it drops its bones.

A lens of oil
Black, with a rainbow sheen, trapped under shale. With a bucket, it becomes fuel — and, refined, kerosene (a real rocket propellant) and plastic.

How deep can you dig?

Heights in Openworld are real altitudes: the sea sits at 160 m and the peaks climb up to 300 m. The floor of the world is the bedrock, at altitude 0 — that is 160 m under the beach, and up to 300 m under a summit. Caves live in the 200 m band under the surface, never in the bedrock.

And the center of the planet? It's 1,000 km further down: out of reach. Since the world is a round planet, “down” always points to that center, wherever you dig — at the equator as at the poles.

Ores by depth: where to find coal, iron, gold and gems

Ore lies in veins: strings of pockets in the rock. Each ore has its own depth band, and some like a particular land above them. The main ones:

• Coal: 3 to 70 m — your torches, your fuel and the Furnace's reducer.
• Copper: 8 to 90 m, more common under highlands.
• Iron: 10 to 140 m — tools, armor, buckets.
• Raisonite: rare violet pockets, 35 to 110 m — the first alloy.
• Gold: 70 to 200 m.
• Titanium: 90 to 200 m, three times as common in volcanic provinces.
• Gems: 100 to 200 m, more common under mountains. The diamond is cut out of gem ore.
• Uranium: 120 to 200 m.

Bauxite, lithium, saltpetre, sulfur and flint feed the machines too. When you need ores for your armor, you now know how far to go; all of them, with the lands they like, are in our resources guide.

• 200meters of caves under the surface
• 19kinds of ore in the veins
• 134giant lodes on the Earth
• 14meters lit by one torch

Coal and iron from your very first cave

On top of the big veins, the first 48 m under the ground hold a second, denser network of small coal and iron veins: almost one 6 m cube of rock out of two has one, so every cave wall shows some — about one vein every 25 m of gallery. A full iron armor fits in two or three iron veins. That's why your first nights go so much better with a pickaxe in hand.

Giant lodes and their boulders

Every world also hides giant lodes: about ninety on the Earth, ellipsoids of ore 40 to 120 m wide whose top lies 2 to 30 m under the ground — coal, iron, copper, bauxite, gold, titanium, lithium, uranium, gems, saltpetre and oil. The first coal, iron, copper and bauxite lodes lie between 250 and 700 m from the world's starting point, the others within 1.5 km.

How to spot one: boulders of ore, 2 to 4 m high, standing on the ground above its core. Dig into the middle: the core is pure ore, thinning out toward the rim. Oil is the exception: no boulders, but black seeps of bitumen (see below).

Lava: how not to die

Lava lakes sit deep: domed chambers whose floor is a lake of lava, rimmed with obsidian, magma rock and basalt. Their bottom lies 6 to 30 m above the bedrock, always at least 40 m under the surface. You'll find one in one 220 m stretch of land out of five — one out of two in volcanic provinces. Some flooded caves fill with lava instead of water, too, when their level is deep enough.

Lava lights 12 m around it, so its orange glow warns you from afar. Step into it and you burn, again and again, and your health melts: a few seconds is enough. Armor softens the burns, it doesn't save you. The death screen sums it up: “You tried to swim in lava.”

Oil and what it's for

Oil sleeps in two kinds of fields. Giant oil fields lie under the lowlands — plains and gentle land away from the mountains: one within 6 km of the world's start, eight more around the planet. Their sign is on the ground: three to five oil conduits climb all the way to the surface, each capped with black bitumen in a ragged patch 1 to 3 m wide. Dig through it and follow the pipe of oil down to a lens about 120 m wide, its top some 30 m under the ground.

Small lenses — 20 to 60 m wide, 6 to 16 m thick, centered 20 to 60 m down, trapped under a cap of shale — show nothing at the surface. Thin conduits climb from their roof and stop 2 to 8 m under the ground in a stain of bitumen: dig, and when your pickaxe meets bitumen or dark shale, the oil is below. In a cave, a black bitumen pillar between floor and ceiling is the same conduit: follow it down. Look under deserts, plains and plateaus; never under volcanoes or high mountains.

A little air sits on top of every lens, and bitumen can be lit with a torch: it then burns forever, a beacon over your oil. All the signs, step by step, are in our resources guide.

To bring it up, you need a bucket (three iron ingots): one cubic meter of a single liquid at a time. Then the refinery, a copper column over a fire, splits oil into:

• Kerosene, and RP-1 for real rockets once poured into a dewar;
• Petrol and diesel, fuels for your generators;
• Natural gas, liquefied into methane at the gas plant;
• Plastic (on another setting), for circuit boards, batteries and cables, and tar.

Raw oil also burns in a fuel slot (20 seconds per cubic meter). And if you dream of pumps and conveyors, see what oil is for in a factory.

Crystals, geodes and stalactites

From 20 to 160 m down, your pickaxe may break into a geode: a hollow sphere 4 to 9 m across, a calcite shell lined with glowing crystals, quartz and a few gems. Crystals give off a cold light that reaches 5 m, like the blue glowing mushrooms of lush caves: in the dark, they're your landmarks.

Stalactites hang in calcite from the ceilings of dripstone caves, in packed ice in frozen caves; in deep caves, crystal clusters take their place.

What lives down there

Underground, it's always night. Creatures of the dark come out in caves at any hour, from 6 m down to about 50 m under the surface. Who you'll meet:

• Bats (hostile): in groups of 2 to 5, they swoop down on you. They drop guano.
• Zombies, slimes and shroomers (hostile): the night's regulars, at home underground.
• Spiders (neutral): leave them alone and they leave you alone. Their string makes your bow.
• Trolls (hostile): 2.6 m tall, slow and hard-hitting. Some carry a diamond.
• Magma golems (hostile): they glow, and they're five times more likely next to lava.
• Crystal golems (neutral): huge and glowing, peaceful as long as you don't hit them.
• Fire salamanders (neutral): a cone of fire, and a fire gland for you if you win.
• Imps (hostile), scorpions (neutral) and harmless sporelings complete the cast.
• The mimic chest: a chest… that bites. Beat it for iron and gold ingots, arrows, and sometimes a diamond.

The surface has its own crowd at night: see monsters in the dark.

Light and getting back out

Far from the entrances, it's pitch black. Your light comes from what you bring: a torch (one voxel of coal on a stick makes four) lights 14 m around it, a lantern (a torch under an iron cage) gives the same reach in white — and no monster spawns in their light. Down there, only lava (12 m), crystals and glowing mushrooms (5 m) shine on their own.

1. 1

   Pack torches and food

   Craft a good stack of torches before going down: coal shows up on the first walls, so you can refill on the way.

2. 2

   Mark your way

   Place a torch at every fork, always on the same side as you go down: no monster spawns within 14 m of it. To come back, keep them on the other side.

3. 3

   Mine as you go

   Coal and iron line the first tens of meters. A better pickaxe — wood, stone, iron, titanium — digs faster and lasts longer.

4. 4

   Watch your step

   A fall hurts from 3 m, and every extra meter costs you more health. Ravines and shafts are deeper than they look in the dark.

5. 5

   Respect liquids

   In a flooded cave you hold your breath 15 seconds, then you start to drown. Near lava, keep a voxel of rock between it and your feet.

6. 6

   Dig your way up

   Lost? Cut stairs into the rock toward the surface. Caves never go deeper than 200 m under the ground: the sky is always within reach.