Hardened Lava Wall is a dark maroon building-block with amber fiery glowing bits. You can craft it in your Crafting Menu (default key "q") after finding the according rare Recipe (loot from the Thing or found in Iron Treasure Chests on blocks of the Lava layer or in Diamond Treasure Chests on corrupted blocks, like in the Corruption layer). Recipes can also be learned in player-created Adventures.
The block can be rotated by pressing and holding R and moving the mouse while holding the left mouse button.
To craft 8 (blocks of) Hardened Lava Walls at a time you'll need (as of R44 in June 2017):
- 4 Hardened Lava blocks mined from the Lava layer with at least an Iron Mining Cell equipped (or made from Igneous Rocks with Fire Bombs, or from liquid Lava by cooling it down)
- 2 Iron Rods made from Iron Bars in a Processor. Iron Ore can be extracted from Nodes found on the Stalactite layer or can also be collected from Iron Treasure Chests or Diamond Treasure Chests
- 1 Glob of Goo (made from Mold in a Processor or obtained from many Creatures as a loot or pet-harvest)
- 1 (block of) Igneous Rock mined from the Lava layer with at least an Iron Mining Cell equipped (or made from Hardened Lava by cooling it down)