1. Western Wall Tunnels, Jerusalem — Old City, Jerusalem
The full length of the Herodian wall, underground — guide-only, and the best hour in the Old City.
The visible Western Wall is a fraction of the retaining wall Herod built around the Temple Mount. The tunnel route runs north along the buried remainder, past the Western Stone — a single block weighing several hundred tonnes — and through Second Temple street level and later Mamluk vaults.
Entry is only with a guide on a timed ticket booked through the Western Wall Heritage Foundation, and slots sell out days ahead in high season. The route is narrow in places and involves stairs.
It is the tour that most changes how you read the rest of the Old City, because it shows you how much of it is stacked on top of something older.
Good to know: Book online weeks ahead in spring and autumn — the timed slots genuinely sell out.