Kungliga Slottet was built on the ruins of Tre Kronor castle, which burned down in 1697. The north wing survived and was incorporated into the new building. Designed by court architect Nicodemus Tessin the Younger, it took 57 years to complete. Highlights include the decadent Karl XI Gallery, inspired by Versailles’ Hall of Mirrors, and Queen Kristina’s silver throne in the Hall of State.
With 608 rooms, this is the world’s largest royal castle still used for its original purpose. The first royal family moved here in 1754. The palace is not a museum but rather a working government building; though it contains fine examples of baroque and rococo furnishings and interiors, each room also bears the fingerprints of the many generations who have lived here. Engaging 45-minute guided tours (adult/child 20kr/free) are held two to three times daily; check the website for the timetable.
Admission to the palace also includes the Museum Tre Kronor, devoted to Stockholm's original castle; the Royal Treasury; and Gustav III's Antikmuseum (the museum of antiquities).
In the basement Museum Tre Kronor, you can see the foundations of 13th-century defensive walls and items rescued from the medieval castle during the 1697 fire. The museum also describes how the fire started (a fire watcher was off flirting with a kitchen maid, it seems) and explains rather vividly the meaning of 'run the gauntlet' (which in 1697 was how the court punished watchmen for flirting with kitchen maids while fire destroyed the castle).
The Royal Treasury contains ceremonial crowns, sceptres and other regalia of the Swedish monarchy, including a 16th-century sword that belonged to Gustav Vasa. Gustav III’s Antikmuseum (closed mid-September to mid-May) displays Italian sculptures collected by King Gustav III in the 1780s.
It's worth timing your visit to see the Changing of the Guard, which takes place in the outer courtyard at 12.15pm Monday to Saturday and 1.15pm Sunday and public holidays from late April to August, and 12.15pm Wednesday and Saturday and 1.15pm Sunday and public holidays from September to late April.
The apartments are occasionally closed for royal business; closures are noted on the website.