Founded around 1030, Christ Church is Dublin’s oldest cathedral and a magnificent medieval survivor at the heart of the old city. Its vast stone crypt, one of the largest in Britain and Ireland, holds curious treasures including a mummified cat and rat nicknamed Tom and Jerry. The choir is renowned, and evensong is a moving experience. Climb to the belfry for a hands-on bell-ringing tour if you can, and allow an hour to explore the crypt.