Hallwyl Castle, Water castle in Seengen, Switzerland

Hallwyl Castle is a water castle in Seengen, in the canton of Aargau, Switzerland, built on two islands within the River Aabach and enclosed by fortified walls. The complex brings together residential buildings and defensive structures, all connected across the water by bridges and passages.

The castle was built in the 13th century as a fortified residence and was destroyed by Bernese troops in 1415 during the conquest of Aargau. The reconstruction that followed gave the complex much of the form visitors see today.

The castle was the seat of the Hallwyl noble family, who shaped the region for centuries and left behind a large collection of artworks and furnishings. Walking through the rooms today, visitors can get a sense of how aristocratic daily life looked inside a fortified island residence.

The castle is open Tuesday to Sunday and on public holidays from 1 April to 31 October. The bus stop "Schloss Hallwyl" on line 395 to Lenzburg and Teufenthal lies on the main road; Boniswil station on the Seetalbahn is a 15-minute walk away, and the Seengen boat landing 10 minutes. The rear island is reached only by a bridge from the front island.

The castle hosts Switzerland's largest colony of jackdaws, with over 80 breeding pairs counted in 2015, according to the Swiss Ornithological Institute in Sempach. In summer 2006 poisoned grain reduced the colony by two thirds; the act was never solved, and the birds have since recovered. Look for the dark birds around the round tower.