Proton sandwiches are unusual nonclassical carbocations characterized by a five-center, four-electron bonding array which rapidly isomerize to lower energy isomers with three-center, two-electron bonding arrays via hydrogen migration transition states. These reactions are suspected to involve significant contributions from tunneling, even at relatively high temperatures, where tunneling effects are usually minimal. Machine-learning-accelerated ring-polymer, quasiclassical, and classical