One of the most interesting things to do in summer is to visit some interesting places, excursions to castles, small towns, historical monuments, and of course, to caves, of which there are many in Ukraine. Moreover, during the heat of summer, it is cool in caves. RBC-Ukraine tells which caves in Ukraine are a must-see. Optymistychna Cave This cave is listed in the Guinness Book of Records as the largest gypsum cave and the second-longest in terms of total length of cave passages. It is located on the western outskirts of the village of Korolivka, Ternopil region. The total length of the passa…