  Lattice artefacts are used, through modified lattice actions, as a tool to
find the largest instantons in a toroidal geometry [0,L]^3X[0,T] for T to
infinity. It is conjectured that the largest instanton is associated with
tunnelling through a sphaleron. Existence of instantons with at least 8
parameters can be proven with the help of twisted boundary conditions in the
time direction. Numerical results for SU(2) gauge theory obtained by cooling
are presented to demonstrate the viability of the method.
