The mountains surrounding the Italian village of Longarone are awe-inspiring, and the nearby Vajont Dam’s claim to being one of the world’s tallest draws some attention, even though it’s not in use anymore.

But neither of those features explains why a small but steady stream of visitors has been showing up for decades at a site little-known outside Italy. On the night of Oct. 9, 1963, an avalanche poured tons of rock into the reservoir behind the dam, causing a wave that swept into and over the structure and down into the valley below.