Neutrinos are the ideal messenger for high-energy astrophysics. Weakly interacting and uncharged, they propagate undeterred and unabsorbed through the universe. In the last decade, the IceCube experiment has brought us the discovery of a flux of high-energy, TeV-scale neutrinos and through a multi-messenger lens — the combined observations of neutrinos and other messengers like photons — we are starting to see hints of energetic neutrino sources for the first time. At higher energies still, beyond the PeV scale, we can probe the most energetic sources of both neutrinos and cosmic rays, but current neutrino experiments become too small to observe a sizable flux. Radio experiments can achieve the large exposures necessary by taking advantage of the coherent broadband radio emission resulting from ultra-high-energy (E>10^17 eV) neutrino interactions as well as the large volumes visible from high elevations. In this talk, I will review results from current and future high-elevation radio experiments, with a particular focus on Earth-skimming tau neutrinos and cosmic ray air showers as observed with balloon-borne and mountaintop experiments.