  A novel Hamiltonian description of the dynamics of a spherically symmetric,
light-like, self-gravitating shell is presented. It is obtained via the
systematic reduction of the phase space with respect to the Gauss-Codazzi
constraints, model and rare procedure in the Canonical Gravity. The Hamiltonian
of the system (numerically equal to the value of the ADM mass) is explicitly
calculated in terms of the gauge-invariant "true degrees of freedom", i.e. as a
function on the reduced phase space. A geometric interpretation of the momentum
canonically conjugate to the shell's radius is given. Models of matter
compatible with the shell dynamics are found. A transformation between the
different time parameterizations of the shell is calculated. The presented
model may become a new toy model of quantum gravity.
