Real-time, physically based rendering of black hole spacetimes in the browser by integrating null geodesics through the curved metric. Choose Schwarzschild (non-rotating), Kerr (rotating, with frame dragging and an asymmetric shadow), or Taub-NUT (carrying a gravitomagnetic NUT charge). The simulation shows gravitational lensing of the background star field, a Doppler-beamed and gravitationally redshifted accretion disk, the photon ring and the black hole shadow. Drag to orbit the camera, scroll to zoom, and adjust the spin, NUT charge, field of view, integration quality and supersampling.