Tin Brick Wall

The copies that generate in Jungle Shrines count as safe walls. Most background walls placed by world generation let enemies spawn behind them, so a shrine is one of the rare underground rooms you can convert straight into a base without stripping the background and re-walling it by hand.

Crafted copies behave the same way, so you can extend a shrine outward and keep the spawn protection. If you like the metal look for an underground house, this is one of the few such walls made from an ore you usually have spare by the time you need it.