Traditional 3D rendering pushes triangles through a pipeline. Raymarching skips geometry entirely: for every pixel, a ray walks forward from the camera in steps, asking at each point “how far is the nearest surface?” until it hits something. The answer comes from a signed distance field, a function that returns distance-to-surface for any point in space, and the safe-step version (march exactly as far as the nearest surface allows) is called sphere tracing.
Because the whole scene is one mathematical function inside a fragment shader, forms impossible or expensive as triangles fall out almost free: infinitely repeating structures, smooth blends between shapes, fractals with endless detail, spaces that fold and warp. This is how demoscene productions and Shadertoy shaders conjure entire worlds from a few hundred lines with no models, no meshes, no assets.
The costs are compute (every pixel marches its own ray, many steps deep) and a particular skill set, since modeling means writing math rather than sculpting. For live visuals, raymarched scenes are prized because their parameters are just numbers in a formula, and numbers are exactly what audio analysis produces: a kick can literally bend space.