Eggert Achen (30 November 1853 in Kvislemark - 20 December 1913 in Aarhus) was a Danish architect, brother of the painter Georg Achen.
Chairman of the Architects' Association of Denmark between 1910 and 1914, he was a Freemason and member of the Danish Masonic Order. He designed several lodges for the Freemasons including one in Randers in 1881, together with Frits Uldall, and in Aarhus in 1908. He collaborated frequently with the Aarhus architect Thorkel Møller, mainly in Central and South Jutland in the restorations of manors and hotel conversions. Varna Palæet, a restaurant, and the Technical School in Hobro can also be counted amongst his works.