Name and Location

The Understen Lighthouse, also known as "9FGW7WG9+2X", is located in Grisslehamn, Norrtälje Municipality, Stockholm County, Sweden (60.2750958° N, 18.9199452° E).

Construction and History

The Understen Lighthouse was constructed at an unknown date, but has been an important part of maritime history ever since.

Architecture and Materials

The lighthouse stands at a height of 34 meters (112 feet) and features a unique architectural style characteristic of its era. The structure is made of [construction materials], which have withstood the test of time despite exposure to harsh marine environments.

Light and Navigation

• Fl(3)W.15s: The primary light has a green color and a range of 15 nautical miles (27.8 km). It rotates every 15 seconds.
• F.34.15: The secondary light has a white color and a range of 15 nautical miles (27.8 km).
• F.34.9: The third light has a red color and a range of 9 nautical miles (16.7 km).
• Fl(4).48.23: The fourth light is a group of four lights, each with a white color and a range of 23 nautical miles (42.6 km).

Accessibility and Visiting

Visitors can access the lighthouse grounds, but the interior is not open to the public. The nearest town is Grisslehamn, which offers basic amenities and services.

Notable Views and Landscape

The lighthouse stands on a rocky outcrop overlooking the Baltic Sea. The surrounding landscape is characterized by rolling hills, forests, and meandering waterways.

Technical and Operational Details

The lighthouse has been automated since an unknown date, ensuring continuous operation without the need for manual intervention.

Further Information

• 1. United States National Geospatial-Intelligence Agency (US NGA) Publication 116 (2022-06-03)
• 2. Swedish Maritime Administration (SMA) reports and publications