With the exception of Cardiff Castle, St John the Baptist Church is the oldest building in the city. The church originally dates back to 1180 but was destroyed in 1404 during the Welsh Revolt and rebuilt thereafter in Gothic style. Now it serves as an Anglican church and is open to the public for prayer or visit.

Headquarters of the Roman Catholic Church and home to the Pope, the Vatican City is an ecclesiastical state and the smallest state in Europe, both in dimension and population. Though teeny tiny, the state holds 11 noteworthy museums, including the Michelangelo-decorated Sistine Chapel (perhaps the greatest gem), St Peter's Basilica, and St Peter's Square. Marvel at the Vatican's treasures with your booked-ahead tour and avoid lining up in notoriously slow-moving queues.

This walled fortress boasts 2000 years of history. Originally a Roman fort, the castle was rebuilt after the Norman conquest and served as a keep until the 18th century, when it became the home of the Bute family, who renovated it in Gothic Revival style. You can walk around the Norman keep, discover the Roman foundations and take a guided tour around the grand apartments with their gilt ceilings and murals.

Beautiful against the backdrop of the Sydney Harbour, the World Heritage-listed Sydney Opera House is a thriving hub of art, culture, and history. As "one of the indisputable masterpieces of human creativity, not only in the 20th Century but in the history of humankind," according to a World Heritage report, it attracts millions of visitors from all over the world each year. Experience all the Sydney Opera House has to offer by taking a guided tour, watching a show, and enjoying a cocktail at Opera Bar at sunset or delicious food in the acclaimed Bennelong Restaurant.