Japanese: 温泉 （おんせん）
A true onsen is a public bathing area that is located on the site of a natural hot spring. Since there is a huge demand for onsens and not enough hot springs to go around, there are also lots of onsens that have their water pumped in from regular sources and heated.
There is one true onsen in Tsukuba (on Mount Tsukuba) and the rest (Tsukuba You World, Yuranosato in Tsuchiura, etc.) should probably be classified as Super Sento.
See also...[]
Links[]