The more-than-3,000-year-old city of Nessebar dots a rocky Bulgarian peninsula on the Black Sea. After being settled by Thracians during the Bronze Age, the city was later colonized by Greeks in 6 B.C.E. It stands as an informative testament to the various civilizations that inhabited this narrow stretch of land, with archaeological and architectural highlights including a Greek acropolis, a temple to Apollo, a ninth-century basilica and a Middle Age fortress [source: UNESCO].
As if the wear and tear that comes with hosting residents – and, more recently, tourists – for more than 30 centuries wasn't enough, rising seas have already claimed about one-third of the ancient city's original land mass. Today, Nessebar stands at about 0 to 59 feet (18 meters) above sea level [sources: UNESCO, National Institute of Immovable Cultural Heritage].