Lighthouse Blunder Creates World's Strangest Border: Market Island's S-Shaped Divide

• Market Island in the Baltic Sea features a unique S-shaped border between Sweden and Finland.
• The border originated from the 1809 Treaty of Fredrikshamn, which inadvertently split the island.
• In 1885, a lighthouse was mistakenly built by Russia (then ruling Finland) on Swedish territory.
• A 1981 agreement swapped land to keep the lighthouse in Finland while maintaining equal territory and coastline for both nations.
• The border is marked by 10 drilled holes due to harsh weather, and a joint survey is conducted every 25 years for adjustments.