Imposing but not too remarkable on the outside. Catastrophically over-ornamented on the inside. St John’s really needs to be seen or you won’t believe it. Really. It’s extremely ornate, filled with gilt ornamentation, statues, a floor made entirely of marble tombstones throughout, and two original Caravaggio paintings. See if you can find the stone of Mattia Preti, who did a good chunk of the interior artwork (tip: in the entrance to the sacristy.) Advice: get there early. You can buy tickets online to skip the queue, but if you arrive at 9.30 then the queue is only a few people and the interior is much less crowded. Towards midday the queue to get in fills half the square outside.