Abstract: I will present a study of gravitational collapse in confined spaces employing the simplest two-body setting: a system composed of two thin shells in spherical symmetry. This double-shell model exhibits critical behavior and chaotic dynamics, both of which are reminiscent of the turbulent instability of anti-de Sitter spacetime recently observed in the evolution of massless scalar fields. The problem amounts to solving just two decoupled ODEs but it captures highly non-trivial dynamics: depending on initial data, one observes prompt collapse, perpetual oscillations or black hole formation on arbitrarily long timescales. Finally, I will discuss how this extremely simple shell model heuristically supports the idea that the cascade of energies to shorter length scales is the mechanism responsible for black hole formation after multiple bounces.