Step back in time at Christ Church, the city's original medieval cathedral, right in the heart of old Dublin. You'll be captivated by the stunning Gothic architecture of the main nave before you descend into the past in the expansive 12th-century crypt, one of the oldest in Ireland. Down in the cool, stone-walled chambers, you'll discover ancient artifacts and the cathedral's most curious residents: a mummified cat and rat. There's an admission fee to enter, but it's well worth it for a glimpse into a thousand years of history. You can also learn how to ring the cathedral bells during special city events.