  Szil\'ard's information engine is a canonical example in the field of
thermodynamics of information. We realize experimentally a macroscopic
many-particle Szil\'ard engine that consists of active particles and use it to
lift a mass against gravity. We show that the extractable work per cycle
increases when the raised weight is changed more gradually during the process.
Interestingly, we find that the ideal extractable work grows with the number of
particles due to giant number fluctuations. This is in contrast to the
calculated behavior of a similar engine operating on thermal particles.
