As well as showcasing spectacular and startling contemporary art, the Venice Biennale is an opportunity to gain access to some of its rarely opened buildings. This year, the Vatican’s pavilion can claim the accolade of most unusual location. If you’ve already visited the canal city, it’s still highly unlikely you’ve entered this building – the Holy See’s exhibition is housed in Venice’s women’s prison. In a sense, the Vatican’s pavilion is a piece of months-long performance art in which the visitor is a participant. The experience is about far more than the art on the walls – it’s about the in…