Santorini, Greece

5 million tourists vs. 15,000 locals. The island is losing.

The blue-dome-white-wall combo that launched a billion engagement posts. Santorini now receives over 5 million visitors annually for a volcanic island with 15,000 permanent residents. Oia's sunset viewpoint is physically dangerous from overcrowding during peak season. The caldera views are genuinely stunning — you just can't see them behind the 200 selfie sticks blocking your sightline.