Auerbach Castle: a fortress originally built by King Charlemagne and then rebuilt by Count Diether IV in the 13th century.
Cologne Cathedral: Also known as the Cathedral Church of Saint Peter, is the world's tallest twin-spired church. Construction began in 1248, but halted around 1560. Construction work began again in the 1840s. And in 1880, the edifice was completed to the original Medieval plan, 632 years after construction began. During my visit, there was a Catholic mass congregation, so out respect, I kept my camera quiet and did not get pictures of the inside.