Hot Lake Hotel (also known as Hot Lake Resort) is an historic Colonial Revival hotel originally built in 1864 in Hot Lake, Union County, Oregon, United States. The hotel received its namesake from the thermal spring lakes on the property, and operated as a luxury resort and sanitorium during the turn of the century, advertising the medicinal attributes of the mineral water and drawing visitors worldwide. It is also the first known commercial building in the world to utilize geothermal energy as its primary heat source.