📜 Holland's earliest sea level marker, dating back to 1684. 🔍 Named after Johannes Hudde, these stones set high water levels for dike and sluice construction. # Why Go 🌊 Witness a key piece of Dutch water management history 📍 See the only original stone remaining in its location 🏛️ See a 350-year-old untouched marker 📏 Discover the basis for European water level measurement (Amsterdam Ordnance Datum) 🚶 Easily accessible in Amsterdam # Why Avoid 💤 A historical marker, not an interactive attraction # Tips 🔎 Located on Eenhoornsluis, at the corner of Korte Prinsengracht and Haarlemmerdijk. 💡 Look for the inscription: “Sea dike height - nine feet and five inches (268 cm) above city water level.” 🚶 A second preserved stone is near Central Station, often missed.