The Bedrock Wall is a plain beige building-block. It can be crafted in your Crafting Menu (default key "Q") or at Crafting Tables (that still exist in worlds created before R22 on September 16th 2015), but only after the recipe has been unlocked upon taking a block of Bedrock for the first time - for example by mining/pulling it from the Fossil layer, which requires at least a Stone Mining Cell. By crafting/taking a Bedrock Wall for the first time, the recipe for Bedrock Doors will be unlocked. To craft 8 (blocks of) Bedrock Walls at a time, you'll need (as of R29 in February 2016):