Black holes are bizarre objects. Everything entering their event horizon stays forever trapped. Yet, black holes are also able to give energy away. This energy powers gamma-ray bursts, and sometimes entire galaxies. Some decades ago, an energy extraction mechanism from black holes was hypothesized by Russian scientist Yakov Zeldovich. This mechanism, known as superradiance, consists in shining a beam of light on a black hole. Under appropriate conditions, the beam is reflected off with higher intensity! But this is all theoretical work, and performing experiments on actual black holes is impossible, for the time being... What we now propose is that a similar effect takes place also in other, more familiar, contexts. In this paper, we propose a feasible experimental setup using a spinning cylinder in the center of a water tank. By carefully choosing the material of the cylinder, arbitrarily large amplifications can be obtained. We also show that, by confining the system, a feedback mechanism develops, triggering an instability which is analogous to a famous kind of instability in black hole physics. Our findings offer the first experimental realization of rotational superradiance and rotational superradiant instabilities, stimulating new research in General Relativity, Fluid Dynamics and Acoustics.