«We estimate that the energy required for the factorization [of the 768-bit RSA challenge at Crypto 2010] would have sufficed to bring two 20° C Olympic size swimming pools to a boil.»
Arjen K. Lenstra, Thorsten Kleinjung and Emmanuel Thomé, “Universal security from bits and mips to pools, lakes – and beyond”, https://eprint.iacr.org/2013/635.pdf