This chapter reviews propagation and feasible applications of strongly localized plasmons in metallic triangular grooves, including channel plasmon-polaritons (CPP) for efficient sub-wavelength guiding and plasmon nano-focusing in tapered metal gaps. Theoretical and numerical analyses of adiabatic and non-adiabatic plasmon nano-focusing in triangular grooves are reviewed, including an important link between nano-focusing and guided CPP eigenmodes. Subsequent numerical analyses have confirmed that similar plasmonic modes also exist in triangular grooves on a metal surface. The additional advantage of CPP modes for achieving high transmission through sharp bends is related to the discussed fact that in triangular grooves radiation losses are additionally impeded by the metal effectively surrounding the bend. CPP modes were launched by the end-fire excitation in the silver-vacuum groove with the cavity. The groove can be regarded as a kind of a waveguide for anti-symmetric gap plasmons with gradually changing effective permittivity.