Siena Cathedral requires a significant amount of time to be truly appreciated, at least 4 hours

Siena is not suitable for a day trip, as it's impossible to see everything in such a short time. The cathedral alone offers twice as much to see as the Florence Cathedral I just visited, and twice as much as Venice's St. Mark's Basilica. It has about ten times more to offer than Milan Cathedral. Beneath the main cathedral lies an even older church that dates back an additional 200 years, and next to the old church is a medieval one. Therefore, the vertical depth is equivalent to about 20 stories, allowing for exploration up and down. The cathedral museum is particularly stunning, housing some of Duccio's finest works. While most cathedrals have exteriors that are more impressive than their interiors (Milan Cathedral being the most typical example), Siena Cathedral is an exception, with an interior that surpasses its exterior in beauty. From the floor to the ceiling, there's also an astonishing library, reminiscent of the Vatican's (from which a Pope originated).