There is no definitive answer to this question as it depends on a number of factors, including the definition of 'room'. However, some contenders for the title of largest room in the world include the Great Hall at Eltham Palace in England, which measures 22m high and 73m long, making it over 1600 square metres in size. The hall was built in the 14th century and was used for grand banquets and other events. Another contender is Hangzhou's Tianyi Chamber, which is said to be China's oldest private library. It measures 28m by 28m, making it just under 800 square metres. The library was built in 1561 and contains over 300,000 ancient texts.