Get tickets in advance to see the interior of Prague Castle (the largest castle in Europe), which features more than 700 rooms. You won’t be able to tour them all, but you can see Old Royal Palace dating back to the 9th century, St. Vitus Cathedral, St. George’s Basilica, the treasury, picture gallery, and Rosenberg Palace, which was built in the mid-1500s. St. Vitus Cathedral is Prague’s largest church and is where the city coronated its kings and queens.