On Sept 18 and 19 there were 119 difficult-to-get-into places in Jerusalem that opened their doors to the public.
Just reading the descriptions of these places is very fascinating!
Under the Western Wall (Hasmonean)
The Kishle (just inside Jaffa Gate — Palace of Herod)
Beneath the Jaffa Gate
The Jerusalem Train Tunnel
and over 100+
The listing of openings can be found here: Jerusalem Open House