The Peace Palace houses the International Court of Justice, the Permanent Court of Arbitration, and the Hague Academy of International Law — making it the most important building in international law. The 1913 neo-Gothic palace, set in a large park on Carnegieplein, is a genuinely beautiful building: red brick and stone, turrets, a clock tower, and gardens that open to the public for free.
Guided tours of the interior run on scheduled days and must be booked in advance — demand is high, so book early. The visitor centre next to the palace tells the story of international justice and the building's history, and is open without prior booking. Even if you can't get into the palace itself, the exterior and grounds are worth a visit, and the combination of architectural grandeur and political purpose is unique. The palace is about 2 km from the Binnenhof, reachable on foot through the embassy district.