Mercer’s castle-like home, Fonthill Museum (525 E. Court St., 215/348-9461, www.fonthillmuseum.org , Mon.–Sat. 10 a.m.–5 p.m., Sun. noon–5 p.m., guided tour only, last tour 4 p.m., $9 adult, $8 senior, $4 child, $12 includes admission to Mercer Museum ) was built 1908–1912.
Modeled after a 13th-century Rhenish castle, it is a mix of medieval, Gothic, and Byzantine styles designed by Mercer himself. Constructed of poured reinforced concrete, the ornate, mazelike interior contains 32 stairways and 44 rooms, each in a different shape.
Mercer’s collection of books, prints, and Victorian engravings are on display, and the ceilings and walls are embedded with handcrafted tiles made in Mercer’s kilns.