10 PRINT CHR$(205.5+RND(1)); : GOTO 10 is a concise and elegant single line of code written in BASIC for the Commodore 64 sometime in the early 1980s. When run, it produces a maze-like pattern on the screen in an endless loop. Sven Dahlstrand rewrote this one-liner for the original Game Boy, written in assembly language using the RGBDS toolchain. ROM, source, and documentation are freely available.

Thanks to Sven Dahlstrand for the hint!