The Tj&ouml;rnin, or the pond, is a lake in Reykjavik. It is popular with locals and water-birds. Geothermal waters keep part of the lake free of ice in the winter. Reykjavik's City Hall, or R&aacute;&eth;h&uacute;s Reykjav&iacute;kur sits on one side of the Tjornin pond. It is home to a giant 3D map of Iceland.