Wolfenbüttel's old town is compact enough to see on foot in a day, but the concentration of high-quality sights — the Herzog August Bibliothek, the castle, the Marienkirche, and the half-timbered streetscapes — makes it worth more time than most visitors give it. The library and castle both have interiors well worth entering; the street wandering is free. Start at the market square (Stadtmarkt) and work outward along the canal streets toward the library.