Approximate location — plotted from published sources, not a site visit, and not a guarantee of access.
Historic sulfur warm springs in Spanish Fork Canyon at the vanished Castilla resort site beside US-6/89. Train-era spa destination of the 1890s–early 1900s; the resort burned in 1942 and was never rebuilt. Today the springs form a roadside sulfurous seep/wetland rather than developed soaking pools — visit as a geothermal historic landscape, not a spa day.