I have been living in a flat, right near Paris, for the last 16 years.
You don't see your neighbours if you don't want to !
Going to work early, coming back late, you almost never get to see them.
So I knew a few faces, not always the attached names, and anyway didn't know on which floor they lived !
3 years ago, I decided to join the national campaign "Immeubles en fête" (= buildings celebration or more exactly neighbours' celebration).
This year, we had our third "fiesta" on may, 31st, and half of the flats in my building were represented : one familly come with the main dish, another comes with wine, or dessert a.s.o. ; everyone brings something.

Now I know at least half of my neighbours and I have solved the problem I had with my cat when obliged to leave for a few days : one familly has also cats and dogs and is always happy to act as a catty sitter for my pet...

This "Neighbours' celebration" idea has been launched in 1999 by a frenchman living in Paris and sad not to have more relationship with his neighbours.
He organised a small "fiesta" within his building, next within the city block, then get in touch with municipalities and his idea gained more and more popularity.
in 2005, the idea has been promoted in a dozen european capitals and an estimated 4,000,000 people participated.