This 17th-century church was once part of the nearby cathedral. It's a mishmash of different architectural styles, from baroque to neoclassical. The Solomonic columns on the outside are both Ionic and Gothic. Inside, you can see the Moorish influence in the painted domes, with their striking frescos. As you enter El Sagrario, look down -- you will see crypts. (Those with crossbones mean that the body buried there died of smallpox.) The second door is regarded as a colonial-era masterpiece; it was painted with liquid gold leaf and designed with vegetables and fruits, including pineapples, which are considered an indigenous welcome symbol. The lovely and intricate rococo altarpiece is also impressive -- it took 12 years to build. Give yourself 15 minutes here (a half-hour, if you want to linger).