South Pole Telescope.

The largest telescope ever is up at the South Pole, funded by the National Science Foundation. The South Pole Telescope is designed to measure the properties of the Cosmic Microwave Background (CMB) light that was originally created billions of years ago in the infant universe. It will search for galaxy clusters in order to try to confirm the existence of Dark Energy and find out something about its properties. Scientists hope this may lead to new understanding of the age, nature, and future of the universe.

Why put a telescope at the South Pole? Because 1. the dry conditions make the atmosphere extremely clear, 2. the altitude is two miles high, putting the South Pole above the sea's vapor level, and 3. the lack of sunlight in the polar winter makes it easier to search the sky. Link -via Metafilter