We present VLA observations of the luminous radio galaxy 3C 295 at 2, 3.6, 6, and 20 cm. The combination of its extreme luminosity with small physical size results in a very high energy density and equipartition magnetic field strengths of approximately 500-mu-G. The spectrum is unusually steep for a radio galaxy, and shows curvature at all frequencies. In addition, we find the largest Faraday rotation measures (RMs) yet measured in an extragalactic source, exceeding 20 000 radians m-2 in places. We believe these RMs are caused by cluster gas and magnetic fields of strength approximately 30-mu-G, and are not produced within the source or at its boundary. We suggest that this is a young radio galaxy, less than 2 million years old.