  We report on a numerical study of gravitational waves undergoing
gravitational collapse due to their self-interaction. We consider several
families of asymptotically flat initial data which -- similarly to the well
known Choptuik's discovery -- can be fine-tuned between dispersal into empty
space and collapse into a black hole. We find that near-critical spacetimes
exhibit behavior similar to the collapse of scalar field: For different
families of initial data we observe universal `echoes' in the form of
irregularly repeating approximate scaled copies of the same piece of spacetime.
