The Illustris Project was a series of cosmological simulations
(simulations of the universe)
that began with conditions created by the Big Bang
and ran to the current day, producing data-snapshots that
correspond in many ways to the observable universe.
In visual form, some of these data-snapshots are now popular
illustrations and videos used to explain various aspects of the
universe's history.
The code was AREPO.
The main simulation used 19 million cpu hours.
The IllustrisTNG Project is a subsequent series of simulations
modeling more effects, begun in 2016.