The Western Wall in Jerusalem is the only wall remained intact after the destruction of the Second Temple located in the Temple Mount. The western Wall is considered the most sacred site recognised by Judaism outside the Temple Mount itself.
A well known Jewish custom is placing a piece of paper contains blessing or wish (for good health, for peace etc). Here is a SS issued by Israel on March 26, 1979, to publicize the signing of the peace treaty between Egypt and Israel, depicting a piece of paper contains blessing for peace, placed between the Western Wall stones:
Pope John Paul II placing a piece of paper contains blessing for peace (written on the tab) inside the Western Wall stones. Issued by Israel on May 18, 2005:
Priestly Blessing is a Jewish religious custom takes place at the Western Wall during the Passover and Sukkot Jewish holidays as depicted in this stamp issued by Israel on September 27, 2005:
Jews praying in front of the Western Wall, from the set "children paint Jerusalem", issued by Israel on November 13, 1979: