what is the significance of this wall?
It is the holiest place where Jews are permitted to pray and the Foundation Stone - the most sacred site in the Jewish faith - lies behind it. For Muslims, it constitutes the eastern border of "al-Haram al-Sharif", the Noble Sanctuary of the Al-Aqsa Mosque.
Western Wall
In one of several varying Muslim traditions, it is the site where the Islamic Prophet Muhammad tied his winged steed, al-Buraq, on his Isra and Mi'raj to Jerusalem before ascending to paradise, and constitutes the eastern border of "al-Haram al-Sharif", the Noble Sanctuary of the Al-Aqsa Mosque.

The Western Wall's holiness in Judaism is a result of its proximity to the Temple Mount. Because of the Temple Mount entry restrictions, the Wall is the holiest place where Jews are permitted to pray, though the Foundation Stone, the most sacred site in the Jewish faith, lies behind it. 
the distance between the western wall and the dome of the rock is approximately UNANSWERABLE
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Western Wall [SEP] Introduction
In one of several varying Muslim traditions, it is the site where the Islamic Prophet Muhammad tied his winged steed, al-Buraq, on his Isra and Mi'raj to Jerusalem before ascending to paradise, and constitutes the eastern border of "al-Haram al-Sharif", the Noble Sanctuary of the Al-Aqsa Mosque. The Western Wall's holiness in Judaism is a result of its proximity to the Temple Mount. Because of the Temple Mount entry restrictions, the Wall is the holiest place where Jews are permitted to pray, though the Foundation Stone, the most sacred site in the Jewish faith, lies behind it. The original, natural, and irregular-shaped Temple Mount was gradually extended to allow for an ever-larger Temple compound to be built at its top.