A small terraced park on top of the southern city wall, with hundreds of pigeons that have been kept by the city since the eighteenth century. Wall niches are full of them; little vending stalls sell paper cups of seed. You can stand on the parapet and look out over San Juan Bay while pigeons land on your head, which is a more interesting twenty minutes than it sounds.
Free to enter. Late afternoon is best — the heat is off the stone, the cruise ships in the bay catch the sun, and the small esplanade fills up with locals and a few tired travellers happy to sit down.