A block of copper has been cooled to -273.144 °C and kept there for 15 days with a little help from the ancient Romans. The achievement set a new record for cold temperatures on a macroscopic object.

It is impossible, under the third law of thermodynamics, to achieve temperatures of absolute zero (0K or -273.15 °C), but this hasn't stopped attempts to get ever closer to the mark. Heat is the energy of vibration of atoms or molecules so at absolute zero, molecules stop moving. Records for super low temperatures are usually set with small samples of atoms and if lasers are used to counterbalance these motions, collections of atoms can be brought to a near standstill.

Using evaporative cooling to get atoms to temperatures of 0.003K and then lasers the rest of the way, rhodium atoms have been cooled to less than a billionth of a degree. The processes won the 1997 Nobel Prize for physics and laid the foundation for work that won the same award four years later. 

You would need some pretty amazing lasers to get 400kg of copper to those sorts of temperatures, but the Cryogenic Underground Observatory for Rare Events (CUORE) in Italy got their block to 0.006K. They encased the material in a container they describe as, “The only one of its kind in the world, not only in terms of its dimensions, extreme temperatures and cooling power, but also for the selective materials and for the building techniques that both guarantee very low levels of radioactivity." 

Besides being the epitome of cool science, the work wasn't done because CUORE wanted their name in the Guinness Book of Records. The block is being used to detect rare forms of radioactivity, including a yet to be confirmed process called neutrinoless double-beta decay. Radioactive events can be detected through the slight increases in block temperature, which will be sensed by 1000 tellurium dioxide crystals.

Other forms of radioactivity need to be excluded from the environment both to prevent heat seeping into the block and to keep the noise levels down so that very rare processes can be observed when they happen. The best way to do this is to shield the copper with lead dug out of the ground as long ago as possible, giving time for the effects of other elements in the original ore to diminish. CUORE obtained their lead from a sunken Roman galley. Were it not for the shipwreck, the metal would have been made into coins, water pipes or ammunition for slingshots.

The lowest known temperature occuring without human intervention is 1K in the Boomerang Nebula, not much more than a third of the universal background.