| Demon Altar
|| 3 wide ˣ 2 high
are naturally-occurring crafting stations
found mainly in and around Chasms
in The Corruption
, caves in The Crimson
, and more rarely in other areas Underground
. They are used to craft boss
-summoning items and the Night's Edge
. Altars emit some light, making them easy to spot. They cannot be freed, picked up, placed, or crafted. After a world enters Hardmode
, they can be destroyed, but attempting to hit them with a hammer
before that causes the player to lose half their health, and the Altar will not be affected. Whether the Altar is purple or red depends on whether it is a corruption or crimson world.
After the Wall of Flesh has been defeated in a world, Altars can be destroyed with the Pwnhammer or any superior hammer. Each destroyed Altar causes one type of Hardmode ore to appear in the world, with the appropriate message displaying in the players chat: "Your world has been blessed with (ore)".
If a player attempts to destroy the altar with a lesser hammer, or in a world in which the Wall of Flesh is not yet defeated, the altar will be unaffected and the player will lose half their current health, as stated above.
Smashing Altars always results in Cobalt(Palladium), then Mythril(Orichalcum), then Adamantite(Titanium) ore being generated in respective order. The Altar resets the sequence after Adamantite/Titanium, and continues to cause additional Hardmode ore deposits, thus increasing the distribution of the Hardmode ores with each successive time the player smashes an Altar. Each time an Altar is destroyed, 1-3 Wraiths spawn, regardless of the time of day. When destroying multiple Altars in rapid succession, the resulting Wraith swarm may become difficult to deal with.
Which ores are generated is not determined until you smash a Altar. For example, it is not determined which ore your world has, cobalt or palladium, until the first altar has been smashed. The same goes for Mythril/Orichalcum with the second altar, and Adamantite/Titanium for the third. But once the first three altars are destroyed, the sequence is permanently set. If you get Palladium, Mythril, and Titanium, with your first three altars, your world will always produce those and only those when altars are destroyed.
 Used to craft
 Hardmode ore spawns
- Small maps:
- Cobalt Ore spawns below a depth of 760 feet (380 tiles)
- Mythril Ore spawns below 1,000 depth (500 tiles)
- Adamantite Ore spawns below 1,400 depth (700 tiles), 100 feet (50 tiles) above the depth at which Lava begins appearing.
- Medium maps:
- Cobalt Ore spawns below a depth of 1,100 feet (550 tiles)
- Mythril Ore spawns below 1,400 depth (700 tiles)
- Adamantite Ore spawns below 2,130 depth (1,065 tiles), 170 feet (85 tiles) above the depth at which Lava begins appearing.
- Large maps:
- Cobalt Ore spawns below a depth of 1,270 feet (635 tiles)
- Mythril Ore spawns below 2,000 depth (1,000 tiles)
- Adamantite Ore spawns below 2,930 depth (1,465 tiles), 420 feet (210 tiles) above the depth at which Lava begins appearing.
- Altars cannot be collected as items.
- Altars generate less and less new ores as more are destroyed. The second set of altars create 1/2 as much ore as the first set, the 3rd set creates 1/3 as much as the first, and so on.
- Cobalt(Palladium) is roughly twice as common as Adamantite(Titanium), with Mythril(Orichalcum) halfway between.
- Each time an Altar is destroyed, there is a 66% chance that a single random tile in the rock layer will be converted. Only stone blocks can be converted, and they will be converted to ebonstone, crimstone or pearlstone. This will grow to become a new underground Hallow, Crimson or Corruption if given enough time.
- Altars encountered outside of the Corruption/Crimson on a given map will always be found at a depth of around zero feet.
- Altars have a very small chance of dropping Hallowed Seeds when smashed.
If you die by hitting an Altar repeatedly, an empty death message (just the character name) will be displayed.
If an Altar is on top of sand, then by digging the sand below it, the Altar will disappear.
- Players about to enter Hardmode may benefit by mining paths to several known Altars beforehand, as navigating Hardmode Corruption/Crimson is dangerous at first.
- If you destroy every Altar in a world, it then becomes impossible to use them for crafting (at least within that world). Leaving one that's easily accessible in your world might be wise, there is usually one in the nearest cave from spawn at underground level. Alternatively, you can also create a new world and use Altars there for crafting.
- Players should not destroy all the altars just for ore as the amount of ore spawned reduces for every 3 destroyed altars. And the altar, when smashed, will spawn a tile of corruption or hallow, which will soon grow into a new corruption or hallow.
- 1.2: Worlds which have the Crimson instead of the Corruption will have Demon Altars replaced with Crimson Altars.
- 1.1: When smashed with a Pwnhammer or a Hamdrax during Hardmode, either Cobalt, Mythril, or Adamantite will be spawned in the world. Also, it now has a chance to summon a few wraiths and create additional Underground Corruption or Hallow spreading point somewhere in the world when smashed.
- Pre-Release: Introduced.