Its stones are no more holy, to any of the city's three religions than many others here. For most of its length, you walk alongside a buried extension of the Wailing Wall, the massive retaining wall King Herod built to hold up the platform for his splendid temple. But it has no more, or less, sanctity for the Jews than the exposed Wailing Wall. There is no tradition - yet - of praying against it, though at one point a perennial spring seeps down the wall. "That is the wall wailing," the guide can't resist quipping.
At no stage does the tunnel penetrate the wall to cut under what the Jews revere as the Temple Mount and the Muslims cherish as the Haram al Sharif, the "Noble Sanctuary" from which the Prophet Mohammed miraculously ascended to heaven. Al Aqsa mosque, the third most holy in Islam, stands at the southern end of the mount, but the gate opened last Monday night is 400 yards away from it.
The only Muslim constructions are arches and vaults raised here by the Mamluk conquerors of Jerusalem 12 centuries after Herod, some of which were first uncovered by British army engineers in the late 19th century. They have no religious resonances, but are reminders of a glorious Arab past.
There is also a stretch of a 2,000-year-old paved road, on which Jesus may, or may not, have trodden. But that, too, is not unique. You can walk on similar stones in the open air to the south of the Wailing Wall in an archaeological park.
Most of this has been open to the public for the best part of a decade. Excavation ended in 1985. But a new stretch has now been opened through a tunnel the Hasmonean kings used to pipe water from a reservoir into the city 2,200 years ago.
The only real change last Monday night was that an exit gate was cut at the northern end of the Hasmonean tunnel so that visitors can go in one end and come out the other.
The previous Labour government had refrained from opening it for fear of provoking Muslim violence, which has more to do with national aspirations in the disputed holy city than theology. The Jews were pre-empting the final-status negotiations the Palestinians still hope will bring them in a capital in East Jerusalem. The rest is mayhem.