A mainly modern city, Nuremberg (Nürnberg) has nevertheless managed to retain much of its medieval center. The region’s typical red sandstone forms the fabric of the churches of St Lawrence and St Sebald. Attractions include the Kaiserburg Imperial Castle with its old stables today used as a youth hostel; the City Wall (over 5km/3 miles long) with 80 watchtowers; Dürer’s House; Museum of Toys; Fembohaus (municipal museum); the Post and Communications Museum (with more than 200,000 stamps); Germanic National Museum; German Railway Museum; Town Hall; and the ‘Schöne Brunnen’ Fountain with mechanical clock. The international toy fair and the famous Christmas Fair, Christkindlmarkt, also attract many visitors.