Venngarn Castle is a 17th-century Baroque manor house set in a formal park about 5 km north of Sigtuna, on the shores of Lake Mälaren. The building was constructed for Magnus Gabriel De la Gardie, Sweden's wealthiest nobleman in the 1660s, and later became a royal hunting estate. It is one of the finest examples of 17th-century Swedish Baroque architecture outside Stockholm.
The castle grounds are open and pleasant for walking. The building itself has had a complicated ownership history and has been used at various times as a hospital, a residential school for troubled youth, and a rehabilitation centre. The exterior and park are the main draws for visitors — the combination of the formal gardens, the lakeside setting, and the imposing facade is very fine. Accessible by bicycle from Sigtuna in good weather.