Jungle Wall

The jungle wall you dig past underground and the jungle wall you place yourself are treated as separate things by the spawn code. The natural version does nothing to stop enemies appearing, which is why a jungle base built into an existing cave keeps getting raided no matter how sealed it looks. Placed by hand the same wall counts as player made and blocks spawns properly. Since the natural version drops nothing when you break it, buying is the only way to get the placeable kind.

The Dryad only stocks it in hardmode, so an early jungle base has to make do with something else. Once you have it, clentaminator solutions flip it into the corrupt, crimson or hallowed grass wall, and Green Solution turns any of those back. That last step always returns plain Grass Wall though, so a converted jungle wall can never be converted back into jungle wall.