Näs Castle, Medieval castle ruins on Visingsö Island, Sweden

Näs Castle are stone ruins situated on the southern tip of Visingsö Island in Lake Vättern, Sweden. The walls reach about 4 meters in height and still display floor beam supports roughly 2 meters above ground level, revealing details of the original construction.

Built as a royal residence in the 12th century, possibly by King Sverker I or his son Karl Sverkersson, the castle was Sweden's first national stronghold and served as a royal treasury. In 1318 King Birger Magnusson pledged it to King Eric VI of Denmark; it was burned down after fighting the same year while Birger was in exile.

The ruins display a round tower and a square tower, both built from local schist and sandstone, showing how medieval builders structured their defenses. These remains tell visitors about the fortress design of that era.

The ruins are accessible throughout the year and can be freely explored, though the stones may become slippery in wet conditions. Sturdy footwear is recommended for navigating the uneven terrain.

The fortress served as Sweden's first national treasury during the early 13th century, safeguarding royal and state treasures within its walls. This role made it a site of exceptional importance for Sweden's early development as a nation.