Built in the 1800s, this "mining palace" is one of architect Manuel Tolsá's finest works -- considered a masterpiece of Latin American neoclassicism -- and one of the capital's handsomest buildings. Formerly the school of mining, it's occasionally used today for concerts and cultural events (and, in those cases, the patio is often locked off). When it's open, step inside for a look at the patios and fabulous stonework. Guided tours are available.