The UN International Court of Justice is housed in the Vredespaleis (Peace Palace). A visitor centre details the work of the organisations within. Hour-long guided tours are sometimes offered, but if the courts are in session they are cancelled – check first; you need to book ahead (security is strict). Take tram 1 from HS.
The grand building was donated by American steelmaker Andrew Carnegie for use by the International Court of Arbitration, an early international body whose goal was the prevention of war, which proved elusive as WWI broke out one year after it opened in 1913.