Walls protect inside.
Meaning: This means the walls of the sandcastle keep the inside safe from harm.
Choice of Words: Walls are structures that enclose an area or provide a barrier. Protect means to keep safe from harm. Inside means the inner part of something. When you put them together, "Walls protect inside" describes the function of the walls of a sandcastle, keeping the inside safe from the incoming tide or other external factors.
Alternative Expressions
Related Expressions