The perfect site for astronomical interferometry would be one where the wind speeds throughout the atmosphere were very low, there was little atmospheric turbulence (especially at high altitudes), the seismic activity was negligible and the climate very stable. Perhaps surprisingly, these conditions describe the Antarctic plateau perfectly. At Dome C, for example, the average wind speed at ground level is just 2.7 metres/sec. This, combined with low wind speeds at all altitudes up to the stratosphere, leads to a dramatic increase in coherence times. Despite the extreme cold, the Antarctic plateau is a relatively benign environment. At thermal infrared wavelengths the high elevation (typically over 3000 m), intense cold and exceptional dryness also combine to give greatly increased background-limited sensitivities relative to other sites. This increased sensitivity can be used to further enhance interferometer performance, or can be traded against mirror size to allow for a smaller instrument of the same sensitivity.