Garmin's training format, and far more than a route: heart rate, cadence, laps, calories, all sampled through the workout. Converting it to anything else means deciding which of that to lose, because GPX and GeoJSON have nowhere to put most of it.

Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop a TCX file above and choose afterwards.