What is this red glowing thing I've found in Terraria?
Solution 1:
That's a Crimson Altar, the crimson alternative to the Demon Altar.
It's used as a crafting station to make most pre-hardmode boss items, and Night's Edge.
If you attempt to break it before defeating Wall of Flesh or with a hammer of lesser quality to the Pwnhammer, it will damage you for half of your health.