The best way to plan a day trip from Stockholm is to spend the morning touring the old streets of Sigtuna, followed by an afternoon touring Skokloster, one of the great baroque museums of the north. The village of Skokloster lies at Lake Mälaren, 65km (40 miles) northwest of Stockholm, but only a 26km (16 mile) drive northeast of Sigtuna -- it's signposted.
The great Nicodemus Tessin the Elder, whose name appears frequently in books devoted to European architecture, collaborated with others on this grand pile of baroque architecture (1654-76). Flanked by two towers at each end, which are crowned by cupolas and lanterns, the castle represents perfect symmetry. Its recreation of Sweden's golden age comes across most strongly through the richly decorated apartments, boasting an abundance of stucco ornamentation. Antiques, applied art, tapestries, textiles, ceramics, and even arms are on display. The collection of paintings alone has been called priceless.
Who could afford to buy all this loot? The palace was commissioned by Field Marshal Carl Gustav Wrangel, but he didn't pay for all these objets d'art. They came from the spoils of war. If the weather's fair, you can request a picnic basket at the on-site cafe and enjoy it on the landscaped grounds.