50k towards a learning a new profession/trade?

Many people regret their choice of career, often made at a young age based on misguided academic choices at college. uming you have average academic ability (no astronauts or brain surgeons please!), you have 50k, and the time and ability to retrain in any career, with future financial investment in mind (no pionate struggling artists either!), what would you invest your time and money into learning?