König-Ludwig-Eiche, Natural monument tree in Bad Brückenau, Germany.

König-Ludwig-Eiche is an ancient oak tree in Bad Brückenau known for its impressive size and structure. The wide-spreading canopy, thick trunk, and overall proportions make it a dominant natural feature that draws immediate attention when you approach the site.

The oak was already called Stolze Eiche (Proud Oak) before the mid-19th century, when it was renamed after King Ludwig I, who sought its care during his spa stays. The oldest record of its wooden supports dates from 1838. In the 1960s its longest horizontal branch, 22 metres long, broke out, leaving a deep crack in the trunk.

The oak's names trace its history: it was called Stolze Eiche (Proud Oak) until the mid-19th century, then took the name of King Ludwig I, who sought its care during his spa stays. Its earlier role as a festival, dance and rest place for spa guests ended; no more festivals are held beneath it to spare the tree.

The tree stands near the spa town center and can be easily reached via walking paths. Information boards at the site provide context, and benches nearby allow visitors to rest and enjoy the surroundings.

The hollow trunk is held by about 20 steel cables radiating from the main axis to the horizontal limbs, fixed to threaded rods drilled through the branches. When the longest limb, 22 metres long, broke out in the 1960s, 84 annual rings were counted around an iron ring that had grown into the wood.