サン・ジョヴァンニ洗礼堂
Inside the mausoleum are displayed the original bronze entrance doors, based on the Florence Baptistery doors of Lorenzo Ghiberti. The interior has one of the longest-lasting echoes in the world, a phenomenon dramatically demonstrated to visitors by slamming the entrance doors. Another curiosity of the interior architecture is the "Whispering Wa's" or walls. Two people can stand at either end of one of the curved interior walls, facing away from each other into the niche of the wall, and hold a whispered conversation. The remarkable acoustics of the walls project the sound to the listener at the other side.