Salt mines, a significant category of local, regional, national, and/or European underground heritage, are becoming attractive tourism destinations. This paper examines three cases of salt mining in different European countries, namely Wieliczka in Poland, Campina de Cima in Portugal, and Turda in Romania. They are analyzed in the context of history, typical attributes of their attractiveness, and new uses after the salt extraction was or is going to be stopped, in order to detect their unique values as important assets for both Underground Built Heritage (UBH) and Salt Heritage Tourism (SHT). The results of their comparison show that despite a positive impact related to their protection as cultural and industrial heritage, there are also some negative aspects related to increasing costs of their maintenance and adaptation of salt mines to new functions and to meet the tourism needs. By putting in place measures to enhance the awareness of their values and for activating the local community, the three mines are showcases for the economic outputs for their sites and regions, as well as for increasing knowledge regarding UBH.