Ten stops, about a mile and a half on cobblestones, roughly ninety minutes if you stop and look. Tap any picture to read the story. Tap Listen and your phone reads it aloud in English, so you can keep your eyes on the building.
This in-app browser blocks images from other sites, so the tour falls back to line drawings. The photo links themselves are fine. Open this file in Safari and the real photographs load.
Either way, every stop has a Photos button that opens pictures of that exact building.