Unsafe isn't so unsafe that it disables the borrow checker!

The two main things the compiler allows in an unsafe block but not elsewhere are calling other code marked "unsafe" and dereferencing raw pointers. The net result is that safe code running in a system that's not exhibiting undefined behaviour is defined to continue to not exhibit undefined behaviour, but the compiler is unable in general to prove that an unsafe block won't trigger undefined behaviour.

You can side-step the borrow checker by using pointers instead of references, but using that power to construct an invalid reference is undefined behaviour.

The borrow checker still applies in unsafe { } blocks. What it means (iirc) is that you can do pointer/memory stuff that would otherwise not be allowed. But you still fully adhere to Rust semantics