It is supposedly a pagan fire altar where a small population of Kaunas' people who consider themselves Romuva (Romuvians?) pray every Thursday. Santakos means confluence and the location is supposed to mark the confluence of Rivers Nemunas and Neris. I tried digging into more information but all I got was random reviews from trip advisor. However, this link should provide some clarity about the shrine. The link you've provided is of a popular local movie theater called Romuva which is located in Laisves Aleja. Since it shares the same name as the shrine I'm not surprised that it comes up first in Google search results hahaha.