The Pantheon in Rome is a super cool ancient building that started off as a Roman temple and later became a Catholic church. Built by Emperor Hadrian around 126 AD, this place has a massive concrete dome that's still standing tall after almost two thousand years.

It's got this circular design with a sweet portico and a central opening to the sky called the oculus. People have been visiting this place for ages, and it's one of the best-preserved Roman buildings out there.

Plus, it's been in continuous use as a church dedicated to St. Mary and the Martyrs since the 7th century. You can either buy tickets online in advance or at the booth once you arrive.